Real image mode finder optical system

ABSTRACT

A real image mode finder optical system is constructed to be independent of a photographing optical system and includes, in order from the object side, an objective optical system with a positive refracting power, a field frame located in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power. The real image mode finder optical system has an image erecting means, and the focal length of the objective optical system can be made shorter than that of the eyepiece optical system. In this case, the real image mode finder optical system satisfies the following condition:  
     0.52 &lt;mh/fe &lt;1  
     where mh is the maximum width of the field frame and fe is the focal length of the eyepiece optical system.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a real image mode finder optical systemsuitable for use in a lens shutter camera or an electronic still camerawhich is constructed so that a photographing optical system isindependent of a finder optical system, and in particular, to a realimage mode finder optical system which has a large angle of emergenceand is best adapted for mounting to a compact camera.

[0003] 2. Description of Related Art

[0004] In general, finders constructed to be independent ofphotographing optical systems, used in lens shutter cameras, are roughlydivided into two classes: virtual image mode finders and real image modefinders.

[0005] The virtual image mode finder has the advantage that an imageerecting optical system is not required, but has the disadvantage thatsince an entrance pupil is located at the same position as an observer'spupil, the diameter of a front lens must be increased or the area of avisual field is not defined. An Albada finder of this type allows thearea of the visual field to be definitely set, but has the problem thata half mirror coating is applied to the surface of a lens and thus thetransmittance of the lens is reduced or flare is increased.

[0006] In contrast to this, the real image mode finder is such that theposition of the entrance pupil can be located on the object side, andhence the diameter of the front lens can be decreased. Moreover, byplacing a field frame in the proximity of the imaging position of anobjective lens, the area of the visual field can be defined withoutreducing the transmittance.

[0007] A conventional real image mode finder, however, dose not providea sufficient angle of apparent visual field (hereinafter referred to asan angle of emergence). Specifically, an object to be observed can beviewed only in small size. Thus, when the object is a person, there isthe problem that it is difficult to view the expression of the person. Afinder with a relatively large angle of emergence is disclosed, forexample, in each of Japanese Patent Preliminary Publication Nos. Hei6-51201 and Hei 11-242167. However, even such a finder does not providea sufficiently large angle of emergence.

[0008] A so-called telescope has a large angle of emergence. However,the telescope, which has a high magnification, namely a small angle ofvisual field, cannot be applied to a finder constructed to beindependent of the photographing optical system, used in a common lensshutter camera which has a wide angle of view.

SUMMARY OF THE INVENTION

[0009] It is, therefore, an object of the present invention to provide areal image mode finder optical system in which the angle of emergencecan be increased and compactness can be attained.

[0010] In order to achieve this object, the real image mode finderoptical system according to the present invention is constructed to beindependent of the photographing optical system and has, in order fromthe object side, an objective optical system with a positive refractingpower, a field frame located in the proximity of the imaging position ofthe objective optical system, and an eyepiece optical system with apositive refracting power. The real image mode finder optical systemincludes an image erecting means, and the focal length of the objectiveoptical system can be made shorter than that of the eyepiece opticalsystem. In this case, the real image mode finder optical systemsatisfies the following condition:

0.52<mh/fe<1  (1)

[0011] where mh is the maximum width of the field frame and fe is thefocal length of the eyepiece optical system.

[0012] The real image mode finder optical system according to thepresent invention is constructed to be independent of the photographingoptical system and has, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The real image mode finder optical system includes an image erectingmeans, the objective optical system includes three of reflectingsurfaces of the image erecting means, and the eyepiece optical systemincludes one of reflecting surfaces of the image erecting means so thatan image is erected through four reflecting surfaces comprised of threereflecting surfaces of the objective optical system and one reflectingsurface of the eyepiece optical system. The focal length of theobjective optical system is variable, and when the magnification of thefinder optical system is changed, at least two lens units are movedalong different paths. The focal length of the objective optical systemat the wide-angle position thereof is shorter than that of the eyepieceoptical system. In this case, the real image mode finder optical systemsatisfies Condition (1).

[0013] The real image mode finder optical system according to thepresent invention is constructed to be independent of the photographingoptical system and has, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The real image mode finder optical system includes an image erectingmeans, the objective optical system includes three of reflectingsurfaces of the image erecting means, and the eyepiece optical systemincludes one of reflecting surfaces of the image erecting means so thatan image is erected through four reflecting surfaces comprised of threereflecting surfaces of the objective optical system and one reflectingsurface of the eyepiece optical system. The focal length of theobjective optical system is variable, and when the magnification of thefinder optical system is changed, at least two lens units are movedalong different paths. The focal length of the objective optical systemat the wide-angle position thereof is shorter than that of the eyepieceoptical system. The image erecting means including the three reflectingsurfaces is constructed with two prisms so that each of the prisms hasat least one reflecting surface and one of the entrance surface and theexit surface of each prism is configured as a curved surface with finitecurvature.

[0014] The real image mode finder optical system according to thepresent invention is constructed to be independent of the photographingoptical system and has, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The objective optical system has an image erecting means including fourreflecting surfaces. The focal length of the objective optical system isvariable, and when the magnification of the finder optical system ischanged, at least two lens units are moved along different paths. Thefocal length of the objective optical system at the wide-angle positionthereof is shorter than that of the eyepiece optical system. In thiscase, the real image mode finder optical system satisfies Condition (1).

[0015] The real image mode finder optical system according to thepresent invention is constructed to be independent of the photographingoptical system and has, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The objective optical system has an image erecting means including fourreflecting surfaces. The focal length of the objective optical system isvariable, and when the magnification of the finder optical system ischanged, at least two lens units are moved along different paths. Thefocal length of the objective optical system at the wide-angle positionthereof is shorter than that of the eyepiece optical system.

[0016] This and other objects as well as the features and advantages ofthe present invention will become apparent from the following detaileddescription of the preferred embodiments when taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a perspective view showing of a first embodiment of thereal image mode finder optical system according to the presentinvention;

[0018]FIG. 2 is a plan view of the real image mode finder optical systemof FIG. 1;

[0019]FIG. 3 is a side view of the real image mode finder optical systemof FIG. 1;

[0020]FIG. 4 is an explanatory view of a field frame used in the realimage mode finder optical system of the first embodiment;

[0021]FIGS. 5A, 5B, and 5C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system inthe first embodiment;

[0022]FIGS. 6A, 6B, 6C, and 6D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the first embodiment;

[0023]FIGS. 7A, 7B, 7C, and 7D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the first embodiment;

[0024]FIGS. 8A, 8B, 8C, and 8D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the first embodiment;

[0025]FIGS. 9A, 9B, and 9C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina second embodiment;

[0026]FIGS. 10A, 10B, 10C, and 10D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the second embodiment;

[0027]FIGS. 11A, 11B, 11C, and 11D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the second embodiment;

[0028]FIGS. 12A, 12B, 12C, and 12D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the second embodiment;

[0029]FIGS. 13A, 13B, and 13C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina third embodiment;

[0030]FIGS. 14A, 14B, 14C, and 14D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the third embodiment;

[0031]FIGS. 15A, 15B, 15C, and 15D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the third embodiment;

[0032]FIGS. 16A, 16B, 16C, and 16D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the third embodiment;

[0033]FIGS. 17A, 17B, and 17C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina fourth embodiment;

[0034]FIGS. 18A, 18B, 18C, and 18D are diagrams showing aberrationcharacteristics at e wide-angle position of the real image mode finderoptical system in the fourth embodiment;

[0035]FIGS. 19A, 19B, 19C, and 19D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the fourth embodiment;

[0036]FIGS. 20A, 20B, 20C, and 20D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the fourth embodiment;

[0037]FIGS. 21A, 21B, and 21C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina fifth embodiment;

[0038]FIGS. 22A, 22B, 22C, and 22D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the fifth embodiment;

[0039]FIGS. 23A, 23B, 23C, and 23D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the fifth embodiment;

[0040]FIGS. 24A, 24B, 24C, and 24D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the fifth embodiment;

[0041]FIGS. 25A, 25B, 25C, and 25D are sectional views showingarrangements, developed along the optical axis, at wide-angle, middle,and telephoto positions and with respect to an eyepiece optical system,respectively, of the real image mode finder optical system in a sixthembodiment;

[0042]FIGS. 26A, 26B, 26C, and 26D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the sixth embodiment;

[0043]FIGS. 27A, 27B, 27C, and 27D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the sixth embodiment;

[0044]FIGS. 28A, 28B, 28C, and 28D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the sixth embodiment;

[0045]FIGS. 29A, 29B, 29C, and 29D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the sixth embodiment;

[0046]FIGS. 30A, 30B, 30C, and 30D are sectional views showingarrangements, developed along the optical axis, at wide-angle, middle,and telephoto positions and with respect to an eyepiece optical system,respectively, of the real image mode finder optical system in a seventhembodiment;

[0047]FIGS. 31A, 31B, 31C, and 31D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the seventh embodiment;

[0048]FIGS. 32A, 32B, 32C, and 32D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the seventh embodiment;

[0049]FIGS. 33A, 33B, 33C, and 33D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the seventh embodiment;

[0050]FIGS. 34A, 34B, 34C, and 34D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the seventh embodiment;

[0051]FIGS. 35A, 35B, 35C, and 35D are sectional views showingarrangements, developed along the optical axis, at wide-angle, middle,and telephoto positions and with respect to an eyepiece optical system,respectively, of the real image mode finder optical system in an eighthembodiment;

[0052]FIGS. 36A, 36B, 36C, and 36D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the eighth embodiment;

[0053]FIGS. 37A, 37B, 37C, and 37D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the eighth embodiment;

[0054]FIGS. 38A, 38B, 38C, and 38D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the eighth embodiment;

[0055]FIGS. 39A, 39B, 39C, and 39D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the eighth embodiment;

[0056]FIGS. 40A, 40B, 40C, and 40D are sectional views showingarrangements, developed along the optical axis, at wide-angle, middle,and telephoto positions and with respect to an eyepiece optical system,respectively, of the real image mode finder optical system in a ninthembodiment;

[0057]FIGS. 41A, 41B, 41C, and 41D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the ninth embodiment;

[0058]FIGS. 42A, 42B, 42C, and 42D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the ninth embodiment;

[0059]FIGS. 43A, 43B, 43C, and 43D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the sixth embodiment;

[0060]FIGS. 44A, 44B, 44C, and 44D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the ninth embodiment;

[0061]FIGS. 45A, 45B, 45C, and 45D are sectional views showingarrangements, developed along the optical axis, at wide-angle, middle,and telephoto positions and with respect to an eyepiece optical system,respectively, of the real image mode finder optical system in a tenthembodiment;

[0062]FIGS. 46A, 46B, 46C, and 46D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the tenth embodiment;

[0063]FIGS. 47A, 47B, 47C, and 47D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the tenth embodiment;

[0064]FIGS. 48A, 48B, 48C, and 48D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the tenth embodiment;

[0065]FIGS. 49A, 49B, 49C, and 49D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the tenth embodiment;

[0066]FIGS. 50A, 50B, 50C, and 50D are sectional views showingarrangements, developed along the optical axis, at wide-angle, middle,and telephoto positions and with respect to an eyepiece optical system,respectively, of the real image mode finder optical system in aneleventh embodiment;

[0067]FIGS. 51A, 51B, 51C, and 51D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the eleventh embodiment;

[0068]FIGS. 52A, 52B, 52C, and 52D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the eleventh embodiment;

[0069]FIGS. 53A, 53B, 53C, and 53D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the eleventh embodiment;

[0070]FIGS. 54A, 54B, 54C, and 54D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the eleventh embodiment;

[0071]FIGS. 55A, 55B, and 55C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twelfth embodiment;

[0072]FIGS. 56A, 56B, and 56C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina thirteenth embodiment;

[0073]FIGS. 57A, 57B, and 57C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina fourteenth embodiment;

[0074]FIGS. 58A, 58B, and 58C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina fifteenth embodiment;

[0075]FIGS. 59A, 59B, and 59C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina sixteenth embodiment;

[0076]FIGS. 60A, 60B, and 60C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina seventeenth embodiment;

[0077]FIGS. 61A, 61B, and 61C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system inan eighteenth embodiment;

[0078]FIGS. 62A, 62B, and 62C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina nineteenth embodiment;

[0079]FIGS. 63A, 63B, and 63C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twentieth embodiment;

[0080]FIGS. 64A, 64B, and 64C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twenty-first embodiment;

[0081]FIG. 65 is a plan view of the real image mode finder opticalsystem in the twenty-first embodiment;

[0082]FIG. 66 is a side view of the real image mode finder opticalsystem of FIG. 65;

[0083]FIG. 67 is a rear view of the real image mode finder opticalsystem of FIG. 65;

[0084]FIGS. 68A, 68B, and 68C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twenty-second embodiment;

[0085]FIGS. 69A, 69B, and 69C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twenty-third embodiment;

[0086]FIGS. 70A, 70B, and 70C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twenty-fourth embodiment;

[0087]FIG. 71 is a front perspective view showing the appearance of anelectronic camera in an embodiment of a photographing apparatus usingthe real image mode finder optical system of the present invention:

[0088]FIG. 72 is a rear perspective view of the electronic camera ofFIG. 71;

[0089]FIG. 73 is a sectional view showing the structure of theelectronic camera of FIG. 71; and

[0090]FIGS. 74A, 74B, and 74C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of a photographing zoom lens used in a compactcamera for a 35 mm film (the maximum image height of 21.6 mm).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0091] According to the present invention, when the objective opticalsystem is designed to have the focal length shorter than that of theeyepiece optical system, the magnification of the real image mode fineroptical system can be reduced to ix or less, and as a result, the angleof visual field can be increased.

[0092] Condition (1) in the present invention is related to the angle ofemergence. In order to increase the angle of emergence, it is onlynecessary to increase the size of an image obtained by the objectiveoptical system, that is, the size of the field frame, or to reduce thefocal length of the eyepiece optical system.

[0093] Below the lower limit of Condition (1), the image can be seenonly in small size. On the other hand, beyond the upper limit ofCondition (1), it becomes difficult to grasp the entire area of thevisual field, for example, to quickly determine a picture composition.

[0094] By constructing the finder optical system to be independent ofthe photographing optical system, the value of a maximum width mh of thefield frame can be set, irrespective of the size of an imaging plane.This is particularly advantageous for compact design of the eyepieceoptical system and for the placement of an image erecting means.

[0095] It is favorable that the real image mode finder optical system ofthe present invention is constructed so that the focal length of theobjective optical system is variable, and when the magnification of thefinder is changed, at least two lens units are moved along differentpaths.

[0096] When the objective optical system is constructed so that itsfocal length can be changed, a constant angle of emergence can beobtained, without changing the size of the field frame, even when themagnification is changed.

[0097] When the angle of emergence is increased, the phenomenon of aso-called diopter shift will occur if the back focal position isshifted. However, when at least two lens units are moved along differentpaths to change the magnification, the back focal position of theobjective optical system can be kept to be nearly constant.

[0098] It is desirable that the real image mode finder optical system ofthe present invention satisfies the following condition:

12.0 mm<fe<18.0 mm  (2)

[0099] Condition (2) is provided for the purpose of ensuring a space forplacing the image erecting means and compactness of the whole of thereal image mode finder optical system in a state where Condition (1) issatisfied.

[0100] If the lower limit of Condition (2) is passed, a distance on theoptical axis between the front principal point of the eyepiece opticalsystem and the field frame will be reduced and at the same time, thefinder magnification will be as low as 1× or less. Therefore, a distanceon the optical axis between the rear principal point of the objectiveoptical system and the field frame is also reduced, and it becomesdifficult to place the image erecting means, which is not favorable.

[0101] On the other hand, beyond the upper limit of Condition (2), themaximum width mh of the field frame must be enlarged to increase theangle of emergence. In this case, the objective optical system becomesbulky and the balance between the angle of emergence and the size of thereal image mode finder ceases to be kept, which is unfavorable.

[0102] It is more desirable that the real image mode finder opticalsystem satisfies the following condition:

13.5 mm<fe<16.5 mm  (3)

[0103] It is favorable that the real image mode finder optical system isconstructed so that the objective optical system includes threereflecting surfaces of the image erecting means and the eyepiece opticalsystem includes one reflecting surface of the image erecting means toerect an image with four reflecting surfaces comprised of the threereflecting surfaces of the objective optical system and the onereflecting surface of the eyepiece optical system.

[0104] At least four reflecting surfaces are required for the imageerecting means, and thus if the image erecting means is constructed withfour reflecting surfaces, space efficiency can be improved. When threeof four reflecting surfaces constituting the image erecting means areplaced in the objective optical system, the burden of a space forplacing the image erecting means to the eyepiece optical system islessened, and the number of optical elements constituting the eyepieceoptical system can be reduced. Thus, according to the present invention,a real image mode finder optical system with a large angle of emergencecan be constructed in a state where the arrangement of the eyepieceoptical system is simplified.

[0105] It is favorable that the real image mode finder optical system ofthe present invention is constructed so that the objective opticalsystem has the image erecting means including four reflecting surfacesto erect the image with the four reflecting surfaces of the objectiveoptical system.

[0106] In this case, at least four reflecting surfaces are required forthe image erecting means, and thus if the image erecting means isconstructed with four reflecting surfaces, space efficiency can beimproved. When the image erecting means is placed in the objectiveoptical system, the burden of a space for placing the image erectingmeans to the eyepiece optical system is eliminated, and the eyepieceoptical system can be constructed with a small number of lenses.Consequently, the focal length of the eyepiece optical system can becompletely reduced, and aberration characteristics are easily improved.Thus, according to the present invention, a real image mode finderoptical system with a large angle of emergence can be constructed in astate where the arrangement of the eyepiece optical system issimplified.

[0107] As mentioned above, when the objective optical system is designedto have the focal length shorter than that of the eyepiece opticalsystem, the magnification of the real image mode finer optical systemcan be reduced to 1× or less, and as a result, the angle of visual fieldcan be increased. Condition (1) in the present invention is related tothe angle of emergence.

[0108] Below the lower limit of Condition (1), the image can be seenonly in small size. On the other hand, beyond the upper limit ofCondition (1), it becomes difficult to grasp the entire area of thevisual field, for example, to quickly determine a picture composition.

[0109] When the objective optical system is constructed so that itsfocal length can be changed, a constant angle of emergence can beobtained, without changing the size of the field frame, even when themagnification is changed.

[0110] When the angle of emergence is increased, the phenomenon of aso-called diopter shift will occur if the back focal position isshifted. However, when at least two lens units are moved along differentpaths to change the magnification, the back focal position of theobjective optical system can be kept to be nearly constant.

[0111] At least four reflecting surfaces are required for the imageerecting means, and thus if the image erecting means is constructed withfour reflecting surfaces, space efficiency can be improved. When threeof four reflecting surfaces constituting the image erecting means areplaced in the objective optical system, the burden of a space forplacing the image erecting means to the eyepiece optical system islessened, and the number of optical elements constituting the eyepieceoptical system can be reduced. Thus, according to the present invention,the focal length of the eyepiece optical system can be completelyreduced, and aberration characteristics are easily improved. Also, theobjective optical system has a large number of lenses because of themagnification change, and hence can be designed to ensure a space forincorporating three reflecting surfaces in the objective optical system.Consequently, a real image mode finder optical system which has a largeangle of emergence and is compact in design can be constructed in astate where the arrangement of the eyepiece optical system issimplified.

[0112] It is desirable that the real image mode finder optical system ofthe present invention is constructed so that the objective opticalsystem comprises, in order from the object side, a first unit with anegative power, fixed or moved when the magnification is changed; asecond unit with a positive power, moved when the magnification ischanged; a third unit with a negative power, moved when themagnification is changed; and a fourth unit with a positive power, fixedwhen the magnification is change and including three reflectingsurfaces.

[0113] According to the present invention, it becomes easy to achievecompactness of the whole of the real image mode finder optical systemand to obtain favorable aberration and a large angle of emergence.

[0114] It is desirable that the real image mode finder optical system ofthe present invention is constructed so that the fourth unit includes atleast one prism having at least one reflecting surface, and one of theentrance surface and the exit surface of the prism is configured as acurved surface with finite curvature.

[0115] According to the present invention, a lens function, such as acontribution to the focal length or correction for aberration, as thefourth unit of the objective optical system and an image erectingfunction can be exerted in the same space.

[0116] Furthermore, it is desirable that the real image mode finderoptical system of the present invention is constructed so that one ofthe reflecting surfaces of the prism is configured as a totallyreflecting surface.

[0117] If total reflection is utilized as far as possible with respectto the reflecting surfaces of the prism, the transmittance of the entirefinder can be improved accordingly.

[0118] In the real image mode finder optical system, it is desirablethat each of the first unit, the second unit, and the third unit isconstructed with a single lens.

[0119] According to the present invention, it becomes easy to achievecompactness of the whole of the real image mode finder optical system.

[0120] Moreover, it is desirable that the real image mode finder opticalsystem of the present invention is constructed so that the eyepieceoptical system includes optical elements having two lens functions,providing air spacing between them and has a positive refracting poweras a whole.

[0121] In order to increase the angle of emergence, it is only necessaryto increase the size of an image obtained by the objective opticalsystem, that is, the size of the field frame, or to reduce the focallength of the eyepiece optical system. However, if the field frame isenlarged with respect to the focal length of the eyepiece opticalsystem, the burden of correction for aberration to the eyepiece opticalsystem will be increased, and it becomes difficult to hold goodperformance with a single lens. If three or more optical elements areused, it becomes difficult to obtain compactness of the whole of thereal image mode finder optical system. Hence, in order to diminish thesize of the entire system including the objective optical system, it isdesirable to reduce the focal length of the eyepiece optical system.However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed.

[0122] Thus, in view of good performance, space for placing the imageerecting means, and compactness of the whole of the real image modefinder optical system, it is desirable that the eyepiece optical system,as mentioned above, is constructed with the optical elements having twolens functions, providing air spacing between them.

[0123] Furthermore, it is desirable that the real image mode finderoptical system of the present invention is designed so that the eyepieceoptical system includes, in order from the object side, a prism whichhas the lens function, at least, with respect to the exit surface andbears a part of an image erecting function and a single positive lenscomponent.

[0124] As mentioned above, when an optical element on the field frameside of the eyepiece optical system is constructed with the prism whichbears a part of the image erecting function, space can be effectivelyutilized. Moreover, when the lens function is imparted to the prismseparated from the field frame, the degree of a contribution to thefocal length of the eyepiece optical system is increased, and it becomeseasy to reduce the focal length of the eyepiece optical system.

[0125] It is desirable that the real image mode finder optical system ofthe present invention is designed to impart the lens function to theentrance surface of the prism of the eyepiece optical system.

[0126] Since the entrance surface of the prism of the eyepiece opticalsystem is located close to the field frame, the degree of a contributionto the focal length of the eyepiece optical system is low. However,correction for aberration, notably for distortion, and a pupilcombination of the objective optical system and the eyepiece opticalsystem are favorably compatible.

[0127] It is desirable that the real image mode finder optical system isdesigned so that the reflecting surface of the prism of the eyepieceoptical system is configured as a totally reflecting surface.

[0128] As described above, when total reflection is utilized for thereflecting surface of the prism, the transmittance of the entire systemof the finder can be improved accordingly.

[0129] It is desirable that the real image mode finder optical system ofthe present invention is constructed so that the positive lens of theeyepiece optical system is capable of making diopter adjustment inaccordance with an observer's diopter.

[0130] According to the present invention, a change of the diopterrequired is obtained with a small amount of adjustment. Since thediopter can be adjusted by the positive lens, unlike an element in whichthe optical axis is bent as in the prism, the adjustment can be easilymade.

[0131] In this case, it is favorable that the real image mode finderoptical system of the present invention satisfies Condition (2).

[0132] Condition (2) is provided for the purpose of ensuring a space forplacing the image erecting means and compactness of the whole of thereal image mode finder optical system in a state where Condition (1) issatisfied.

[0133] If the lower limit of Condition (2) is passed, a distance on theoptical axis between the front principal point of the eyepiece opticalsystem and the field frame will be reduced and at the same time, thefinder magnification will be as low as 1× or less. Therefore, a distanceon the optical axis between the rear principal point of the objectiveoptical system and the field frame is also reduced, and it becomesdifficult to place the image erecting means, which is not favorable.

[0134] On the other hand, beyond the upper limit of Condition (2), themaximum width mh of the field frame must be enlarged to increase theangle of emergence. In this case, the objective optical system becomesbulky and the balance between the angle of emergence and the size of thereal image mode finder ceases to be kept, which is unfavorable.

[0135] It is more desirable that the real image mode finder opticalsystem satisfies Condition (3).

[0136] According to the present invention, when the objective opticalsystem is designed to have the focal length shorter than that of theeyepiece optical system, the magnification of the real image mode fineroptical system can be reduced to 1× or less, and as a result, the angleof visual field can be increased.

[0137] When the objective optical system is constructed so that itsfocal length can be changed, a constant angle of emergence can beobtained, without changing the size of the field frame, even when themagnification is changed.

[0138] When the angle of emergence is increased, the phenomenon of aso-called diopter shift will occur if the back focal position isshifted. However, when at least two lens units are moved along differentpaths to change the magnification, the back focal position of theobjective optical system can be kept to be nearly constant.

[0139] At least four reflecting surfaces are required for the imageerecting means, and thus if the image erecting means is constructed withfour reflecting surfaces, space efficiency can be improved. When threeof four reflecting surfaces constituting the image erecting means areplaced in the objective optical system, the burden of a space forplacing the image erecting means to the eyepiece optical system islessened, and the number of optical elements constituting the eyepieceoptical system can be reduced. Thus, according to the present invention,the focal length of the eyepiece optical system can be completelyreduced, and aberration characteristics are easily improved. Also, theobjective optical system has a large number of lenses because of themagnification change, and hence can be designed to ensure a space forincorporating three reflecting surfaces in the objective optical system.Consequently, a real image mode finder optical system which has a largeangle of emergence and is compact in design can be constructed in astate where the arrangement of the eyepiece optical system issimplified.

[0140] The image erecting means including the three reflecting surfacesis constructed with two prisms so that each of the prisms has at leastone reflecting surface and one of the entrance surface and the exitsurface of each prism is configured as a curved surface with finitecurvature.

[0141] When the image erecting means including the three reflectingsurfaces of the objective optical system is constructed with two prismsso that one of the entrance surface and the exit surface of each prismhas a curvature, a lens function, such as a contribution to the focallength or correction for aberration, and an image erecting function canbe exerted in the same space.

[0142] As mentioned above, when the objective optical system is designedto have the focal length shorter than that of the eyepiece opticalsystem, the magnification of the real image mode finer optical systemcan be reduced to 1× or less, and as a result, the angle of visual fieldcan be increased. Condition (1) in the present invention is related tothe angle of emergence.

[0143] Below the lower limit of Condition (1), the image can be seenonly in small size. On the other hand, beyond the upper limit ofCondition (1), it becomes difficult to grasp the entire area of thevisual field, for example, to quickly determine a picture composition.

[0144] When the objective optical system is constructed so that itsfocal length can be changed, a constant angle of emergence can beobtained, without changing the size of the field frame, even when themagnification is changed.

[0145] When the angle of emergence is increased, the phenomenon of aso-called diopter shift will occur if the back focal position isshifted. However, when at least two lens units are moved along differentpaths to change the magnification, the back focal position of theobjective optical system can be kept to be nearly constant.

[0146] At least four reflecting surfaces are required for the imageerecting means, and thus if the image erecting means is constructed withfour reflecting surfaces, space efficiency can be improved. When theimage erecting means is placed in the objective optical system, theburden of a space for placing the image erecting means to the eyepieceoptical system is eliminated, and the eyepiece optical system can beconstructed with a small number of lenses. Consequently, the focallength of the eyepiece optical system can be completely reduced, andaberration characteristics are easily improved.

[0147] Also, the objective optical system has a large number of lensesbecause of the magnification change, and hence the image erecting meanscan be constructed with comparative ease.

[0148] It is desirable that the real image mode finder optical system ofthe present invention is constructed so that the objective opticalsystem comprises, in order from the object side, s first unit with anegative refracting power, moved when the magnification is changed; asecond unit with a positive refracting power, moved when themagnification is changed; a third unit with a negative refracting power,moved when the magnification is changed; and a fourth unit with apositive refracting power, fixed when the magnification is change andincluding four reflecting surfaces. According to the present invention,it becomes easy to achieve compactness of the whole of the real imagemode finder optical system and to obtain favorable aberration and alarge angle of emergence. Also, the four reflecting surfaces of thefourth unit constitute the image erecting means.

[0149] In the real image mode finder optical system, it is desirablethat the fourth unit includes two prisms so that each of the prisms hasat least one reflecting surface and one of the entrance surface and theexit surface of each prism is configured as a curved surface with finitecurvature.

[0150] According to the present invention, a lens function, such as acontribution to the focal length or correction for aberration, as thefourth unit of the objective optical system and an image erectingfunction can be exerted in the same space.

[0151] Furthermore, it is desirable that the real image mode finderoptical system of the present invention is constructed so that one ofthe two prisms has totally reflecting surfaces.

[0152] As mentioned above, when total reflection is utilized as far aspossible with respect to the reflecting surfaces of the prism, thetransmittance of the entire finder can be improved accordingly.

[0153] In the real image mode finder optical system, it is desirablethat each of the first unit, the second unit, and the third unit isconstructed with a single lens.

[0154] According to the present invention, it becomes easy to achievecompactness of the whole of the real image mode finder optical system.

[0155] It is desirable that the real image mode finder optical system ofthe present invention is constructed so that the eyepiece optical systemhas a lens which is capable of making diopter adjustment to anobserver's diopter.

[0156] According to the present invention, a change of the diopterrequired is obtained with a small amount of adjustment, with littledeterioration of performance. Since the diopter can be adjusted by thelens, unlike an element in which the optical axis is bent as in theprism, the adjustment can be easily made.

[0157] In this case, it is favorable that the real image mode finderoptical system of the present invention satisfies Condition (2).

[0158] Condition (2) is provided for the purpose of ensuring a space forplacing the image erecting means and compactness of the whole of thereal image mode finder optical system in a state where Condition (1) issatisfied.

[0159] If the lower limit of Condition (2) is passed, a distance on theoptical axis between the front principal point of the eyepiece opticalsystem and the field frame will be reduced and at the same time, thefinder magnification will be as low as 1× or less. Therefore, a distanceon the optical axis between the rear principal point of the objectiveoptical system and the field frame is also reduced, and it becomesdifficult to place the image erecting means, which is not favorable.

[0160] On the other hand, beyond the upper limit of Condition (2), themaximum width mh of the field frame must be enlarged to increase theangle of emergence. In this case, the objective optical system becomesbulky and the balance between the angle of emergence and the size of thereal image mode finder ceases to be kept, which is unfavorable.

[0161] In this case, it is more desirable that the real image modefinder optical system satisfies Condition (3).

[0162] According to the present invention, when the objective opticalsystem is designed to have the focal length shorter than that of theeyepiece optical system, the magnification of the real image mode fineroptical system can be reduced to 1× or less, and as a result, the angleof visual field can be increased.

[0163] When the objective optical system is constructed so that itsfocal length can be changed, a constant angle of emergence can beobtained, without changing the size of the field frame, even when themagnification is changed.

[0164] When the angle of emergence is increased, the phenomenon of aso-called diopter shift will occur if the back focal position isshifted. However, when at least two lens units are moved along differentpaths to change the magnification, the back focal position of theobjective optical system can be kept to be nearly constant.

[0165] At least four reflecting surfaces are required for the imageerecting means, and thus if the image erecting means is constructed withfour reflecting surfaces, space efficiency can be improved. When theimage erecting means is placed in the objective optical system, theburden of a space for placing the image erecting means to the eyepieceoptical system is eliminated, and the eyepiece optical system can beconstructed with a small number of lenses. According to the presentinvention, the focal length of the eyepiece optical system can becompletely reduced, and aberration characteristics are easily improved.Also, the objective optical system has a large number of lenses becauseof the magnification change, and hence the image erecting means can beconstructed with comparative ease.

[0166] It is favorable that the photographing apparatus according to thepresent invention has the photographing optical system and the realimage mode finder optical system which has been described.

[0167] The real image mode finder optical system according to thepresent invention is constructed to be independent of the photographingoptical system and has, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The real image mode finder optical system includes an image erectingmeans, the objective optical system is capable of having the focallength shorter than that of the eyepiece optical system, and theeyepiece optical system has at least one lens. In this case, a mostobserver's pupil-side lens satisfies the following condition:

v>70  (4)

[0168] where v is the Abbe's number of the most observer's pupil-sidelens.

[0169] The real image mode finder optical system according to thepresent invention is constructed to be independent of the photographingoptical system and has, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The real image mode finder optical system includes an image erectingmeans, the objective optical system is capable of having the focallength shorter than that of the eyepiece optical system, and theeyepiece optical system has at least one lens. In this case, the realimage mode finder optical system satisfies Conditions (1) and (4).

[0170] The real image mode finder optical system according to thepresent invention is constructed to be independent of the photographingoptical system and has, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The real image mode finder optical system includes an image erectingmeans, the objective optical system is capable of having the focallength shorter than that of the eyepiece optical system, and theeyepiece optical system has a cemented lens component including apositive lens element and a negative lens element at the most observer'spupil-side position.

[0171] When the objective optical system is designed to have the focallength shorter than that of the eyepiece optical system, themagnification of the real image mode finer optical system can be reducedto 1× or less, and as a result, the angle of visual field can beincreased.

[0172] When Condition (4) is satisfied, chromatic aberration ofmagnification produced in the eyepiece optical system can be suppressed.

[0173] By constructing the finder optical system to be independent ofthe photographing optical system, the value of a maximum width mh of thefield frame can be set, irrespective of the size of an imaging plane.This is particularly advantageous for compact design of the eyepieceoptical system and for the placement of an image erecting means.

[0174] When the objective optical system is designed to have the focallength shorter than that of the eyepiece optical system, themagnification of the real image mode finer optical system can be reducedto 1× or less, and as a result, the angle of visual field can beincreased. Condition (1) in the present invention is related to theangle of emergence. In order to increase the angle of emergence, it isonly necessary to increase the size of an image obtained by theobjective optical system, that is, the size of the field frame, or toreduce the focal length of the eyepiece optical system.

[0175] Below the lower limit of Condition (1), the image can be seenonly in small size. On the other hand, beyond the upper limit ofCondition (1), it becomes difficult to grasp the entire area of thevisual field, for example, to quickly determine a picture composition.

[0176] When Condition (4) is satisfied, chromatic aberration ofmagnification produced in the eyepiece optical system can be suppressed.

[0177] By constructing the finder optical system to be independent ofthe photographing optical system, the value of a maximum width mh of thefield frame can be set, irrespective of the size of an imaging plane.This is particularly advantageous for compact design of the eyepieceoptical system and for the placement of an image erecting means.

[0178] It is favorable that the real image mode finder optical system ofthe present invention is constructed so that the focal length of theobjective optical system is variable, and when the magnification of thefinder is changed, at least two lens units are moved along differentpaths.

[0179] When the objective optical system is constructed so that itsfocal length can be changed, a constant angle of emergence can beobtained, without changing the size of the field frame, even when themagnification is changed.

[0180] When the angle of emergence is increased, the phenomenon of aso-called diopter shift will occur if the back focal position isshifted. However, when at least two lens units are moved along differentpaths to change the magnification, the back focal position of theobjective optical system can be kept to be nearly constant.

[0181] It is desirable that the real image mode finder optical system ofthe present invention satisfies Condition (2).

[0182] Condition (2) is provided for the purpose of ensuring a space forplacing the image erecting means and compactness of the whole of thereal image mode finder optical system in a state where Condition (I) issatisfied.

[0183] If the lower limit of Condition (2) is passed, a distance on theoptical axis between the front principal point of the eyepiece opticalsystem and the field frame will be reduced and at the same time, thefinder magnification will be as low as 1× or less. Therefore, a distanceon the optical axis between the rear principal point of the objectiveoptical system and the field frame is also reduced, and it becomesdifficult to place the image erecting means, which is not favorable.

[0184] On the other hand, beyond the upper limit of Condition (2), themaximum width mh of the field frame must be enlarged to increase theangle of emergence. In this case, the objective optical system becomesbulky and the balance between the angle of emergence and the size of thereal image mode finder ceases to be kept, which is unfavorable.

[0185] It is more desirable that the real image mode finder opticalsystem satisfies Condition (3).

[0186] It is favorable that the real image mode finder optical system isconstructed so that the objective optical system includes threereflecting surfaces of the image erecting means and the eyepiece opticalsystem includes one reflecting surface of the image erecting means toerect an image with four reflecting surfaces comprised of the threereflecting surfaces of the objective optical system and the onereflecting surface of the eyepiece optical system.

[0187] At least four reflecting surfaces are required for the imageerecting means, and thus if the image erecting means is constructed withfour reflecting surfaces, space efficiency can be improved. When threeof four reflecting surfaces constituting the image erecting means areplaced in the objective optical system, the burden of a space forplacing the image erecting means to the eyepiece optical system islessened, and the number of optical elements constituting the eyepieceoptical system can be reduced. Thus, according to the present invention,the focal length of the eyepiece optical system can be completelyreduced, and aberration characteristics are easily improved. Inparticular, where the focal length of the objective optical system isvariable, the objective optical system, which has a large number oflenses, can be designed to ensure a space for incorporating threereflecting surfaces in the objective optical system. Consequently, areal image mode finder optical system which has a large angle ofemergence and is compact in design can be constructed in a state wherethe arrangement of the eyepiece optical system is simplified.

[0188] It is favorable that the real image mode finder optical system ofthe present invention is constructed so that the objective opticalsystem has the image erecting means including four reflecting surfacesto erect the image with the four reflecting surfaces of the objectiveoptical system.

[0189] At least four reflecting surfaces are required for the imageerecting means, and thus if the image erecting means is constructed withfour reflecting surfaces, space efficiency can be improved. When theimage erecting means is placed in the objective optical system, theburden of a space for placing the image erecting means to the eyepieceoptical system is eliminated, and the eyepiece optical system can beconstructed with a small number of lenses. According to the presentinvention, the focal length of the eyepiece optical system can becompletely reduced, and aberration characteristics are easily improved.In particular, where the focal length of the objective optical system isvariable, the number of lenses constituting the objective optical systemis large, and hence the image erecting means can be constructed withcomparative ease.

[0190] According to the present invention, when the objective opticalsystem is designed to have the focal length shorter than that of theeyepiece optical system, the magnification of the real image mode fineroptical system can be reduced to 1× or less, and as a result, the angleof visual field can be increased.

[0191] When the cemented lens component including the positive lenselement and the negative lens element is placed on the observer's pupilside of the eyepiece optical system, chromatic aberration ofmagnification produced in the eyepiece optical system can be suppressed.

[0192] Also, by constructing the finder optical system to be independentof the photographing optical system, the value of a maximum width mh ofthe field frame can be set, irrespective of the size of an imagingplane. This is particularly advantageous for compact design of theeyepiece optical system and for the placement of an image erectingmeans.

[0193] The real image mode finder optical system according to thepresent invention is constructed to be independent of the photographingoptical system and has, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The real image mode finder optical system includes an image erectingmeans, the objective optical system is capable of having the focallength shorter than that of the eyepiece optical system, and theeyepiece optical system has a cemented lens component including apositive lens element and a negative lens element on the observer'spupil side. In this case, it is favorable to satisfy Condition (1).

[0194] When the objective optical system is designed to have the focallength shorter than that of the eyepiece optical system, themagnification of the real image mode finer optical system can be reducedto 1× or less, and as a result, the angle of visual field can beincreased. Condition (1) in the present invention is related to theangle of emergence. In order to increase the angle of emergence, it isonly necessary to increase the size of an image obtained by theobjective optical system, that is, the size of the field frame, or toreduce the focal length of the eyepiece optical system.

[0195] Below the lower limit of Condition (1), the image can be seenonly in small size. On the other hand, beyond the upper limit ofCondition (1), it becomes difficult to grasp the entire area of thevisual field, for example, to quickly determine a picture composition.

[0196] When the cemented lens component including the positive lenselement and the negative lens element is placed on the observer's pupilside of the eyepiece optical system, chromatic aberration ofmagnification produced in the eyepiece optical system can be suppressed.

[0197] Also, by constructing the finder optical system to be independentof the photographing optical system, the value of a maximum width mh ofthe field frame can be set, irrespective of the size of an imagingplane. This is particularly advantageous for compact design of theeyepiece optical system and for the placement of an image erectingmeans.

[0198] It is favorable that the real image mode finder optical system ofthe present invention is constructed so that the focal length of theobjective optical system is variable, and when the magnification of thefinder is changed, at least two lens units are moved along differentpaths.

[0199] When the objective optical system is constructed so that itsfocal length can be changed, a constant angle of emergence can beobtained, without changing the size of the field frame, even when themagnification is changed.

[0200] When the angle of emergence is increased, the phenomenon of aso-called diopter shift will occur if the back focal position isshifted. However, when at least two lens units are moved along differentpaths to change the magnification, the back focal position of theobjective optical system can be kept to be nearly constant.

[0201] It is also favorable that the real image mode finder opticalsystem of the present invention satisfies the following condition:

vp−vn>10  (5)

[0202] where vp is the Abbe's number of the positive lens elementconstituting the cemented lens component on the observer's pupil side ofthe eyepiece optical system and vn is the Abbe's number of the negativelens element constituting the cemented lens component.

[0203] As mentioned above, when the finder optical system is designed tosatisfy Condition (5), chromatic aberration of magnification produced inthe eyepiece optical system can be suppressed.

[0204] It is more desirable that the real image mode finder opticalsystem of the present invention satisfies the following condition:

vp−vn>20  (6)

[0205] It is favorable that that the photographing apparatus accordingto the present invention has the photographing optical system and thereal image mode finder optical system which has been described.

[0206] Also, in the above description, where the reflecting surface isconfigured as a roof reflecting surface, it is assumed that the roofreflecting surface is constructed with two reflecting surfaces.

[0207] The real image mode finder optical system according to thepresent invention includes, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The real image mode finder optical system has an image erecting means,and the objective optical system includes, in order from the objectside, a first unit with a negative refracting power, a second unit witha positive refracting power, a third unit with a negative refractingpower, and a fourth unit with a positive refracting power so that themagnification of the finder is changed, ranging from the wide-angleposition to the telephoto position, by simply moving the second unittoward the object side and the third unit toward the eyepiece opticalsystem. In this case, the finder optical system satisfies Condition (2).

[0208] The real image mode finder optical system according to thepresent invention includes, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The real image mode finder optical system has an image erecting means,and the objective optical system includes, in order from the objectside, a first unit with a negative refracting power, a second unit witha positive refracting power, a third unit with a negative refractingpower, and a fourth unit with a positive refracting power so that themagnification of the finder is changed, ranging from the wide-angleposition to the telephoto position, by simply moving the second unittoward the object side and the third unit toward the eyepiece opticalsystem. In this case, the finder optical system satisfies Condition (1).

[0209] The real image mode finder optical system according to thepresent invention includes, in order from the object side, an objectiveoptical system with a positive refracting power, a field frame locatedin the proximity of the imaging position of the objective opticalsystem, and an eyepiece optical system with a positive refracting power.The real image mode finder optical system has an image erecting means,and the objective optical system is capable of having the focal lengthshorter than that of the eyepiece optical system. The eyepiece opticalsystem includes, in order from the object side, a prism unit with apositive refracting power and a lens unit with a positive refractingpower so that a most field-frame-side surface of the prism unit with apositive refracting power has a positive refracting power and isconfigured as an aspherical surface with a negative refracting power onthe periphery thereof.

[0210] In order to increase the angle of emergence, it is only necessaryto increase the size of an image obtained by the objective opticalsystem, that is, the size of the field frame, or to reduce the focallength of the eyepiece optical system. However, if the field frame isenlarged with respect to the focal length of the eyepiece opticalsystem, the objective optical system must be also enlarged. Moreover,since the burden of correction for aberration to the eyepiece opticalsystem will be increased, it becomes difficult that good performance ofthe eyepiece optical system and compactness due to a simple arrangementare compatible with each other. Thus, in order to keep the size of thefinder compact and increase the angle of emergence, it is desirable toreduce the focal length of the eyepiece optical system.

[0211] However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed. Consequently, it is necessary that the backfocal distance of the objective optical system is increased to place theimage erecting means there.

[0212] Thus, in the present invention, the objective optical system isdesigned to have, in order to the object side, the first unit with anegative refracting power, the second unit with a positive refractingpower, the third unit with a negative refracting power, and the fourthunit with a positive refracting power. In this way, the back focaldistance of the objective optical system is increased.

[0213] When the objective optical system is constructed as mentionedabove, the focal length of the eyepiece optical system can be reduced,and a real image mode finder optical system which has a large angle ofemergence and is compact in design can be obtained.

[0214] Condition (2) defines a condition for maintaining the balance ofsize between the angle of emergence and the finder. Below the lowerlimit of Condition (2), the distance on the optical axis between thefront principal point of the eyepiece optical system and the field frameis reduced, and it becomes difficult to ensure the space for placing theimage erecting means. In addition, a diopter shift due to the positionshift of the field frame in the direction of the optical axis isincreased.

[0215] On the other hand, beyond the upper limit of Condition (2), theobjective optical system becomes bulky because the image formed byobjective optical system must be enlarged to increase the angle ofemergence. Consequently, the balance between the angle of emergence andthe size of the finder ceases to be kept, which is unfavorable.

[0216] When the magnification of the finder is changed, it is necessarythat a variable magnification function is chiefly imparted to one of atleast two moving lens units and a diopter correcting function involvedin the magnification change is chiefly imparted to the other. In thiscase, the amount of movement of the lens unit having the variablemagnification function becomes larger than that of the lens unit havingthe diopter correcting function, and a mechanism for movement is liableto be complicated and oversized.

[0217] Thus, in the present invention, the finder optical system isconstructed so that the magnification is changed, ranging from thewide-angle position to the telephoto position, by simply moving thesecond unit toward the object side and the third unit toward theeyepiece side.

[0218] By doing so, both the variable magnification function and thediopter correcting function can be shared between the second unit andthe third unit. Hence, the amount of movement of each of the second andthird units where the magnification is change can be kept to a minimum,and compactness of the mechanism for movement is obtained.

[0219] In this case, it is more desirable that the real image modefinder optical system satisfies Condition (3).

[0220] As mentioned above, in order to increase the angle of emergence,it is only necessary to increase the size of an image obtained by theobjective optical system, that is, the size of the field frame, or toreduce the focal length of the eyepiece optical system. However, if thefield frame is enlarged with respect to the focal length of the eyepieceoptical system, the objective optical system must be also enlarged.Moreover, since the burden of correction for aberration to the eyepieceoptical system will be increased, it becomes difficult that goodperformance of the eyepiece optical system and compactness due to asimple arrangement are compatible with each other. Thus, in order tokeep the size of the finder compact and increase the angle of emergence,it is desirable to reduce the focal length of the eyepiece opticalsystem.

[0221] However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed. Consequently, it is necessary that the backfocal distance of the objective optical system is increased to place theimage erecting means there.

[0222] Thus, in the present invention, the objective optical system isdesigned to have, in order to the object side, the first unit with anegative refracting power, the second unit with a positive refractingpower, the third unit with a negative refracting power, and the fourthunit with a positive refracting power. In this way, the back focaldistance of the objective optical system is increased.

[0223] When the objective optical system is constructed as mentionedabove, the focal length of the eyepiece optical system can be reduced,and a real image mode finder optical system which has a large angle ofemergence and is compact in design can be obtained.

[0224] Condition (1) is related to the angle of emergence. Below thelower limit of Condition (1), the image can be seen only in small size.On the other hand, beyond the upper limit of Condition (1), it becomesdifficult to grasp the entire area of the visual field, for example, toquickly determine a picture composition.

[0225] When the magnification of the finder is changed, it is necessarythat the variable magnification function is chiefly imparted to one ofat least two moving lens units and the diopter correcting functioninvolved in the magnification change is chiefly imparted to the other.In this case, the amount of movement of the lens unit having thevariable magnification function becomes larger than that of the lensunit having the diopter correcting function, and a mechanism formovement is liable to be complicated and oversized.

[0226] Thus, in the present invention, the finder optical system isconstructed so that the magnification is changed, ranging from thewide-angle position to the telephoto position, by simply moving thesecond unit toward the object side and the third unit toward theeyepiece optical system.

[0227] By doing so, both the variable magnification function and thediopter correcting function can be shared between the second unit andthe third unit. Hence, the amount of movement of each of the second andthird units where the magnification is change can be kept to a minimum,and compactness of the mechanism for movement is obtained.

[0228] In this case, it is more desirable that the present inventionsatisfies the following condition:

0.57<mh/fe<1  (7)

[0229] As described above, when the objective optical system is designedto have the focal length shorter than that of the eyepiece opticalsystem, the magnification of the real image mode finer optical systemcan be reduced to 1× or less, and as a result, the angle of visual fieldcan be increased.

[0230] When the eyepiece optical system is designed to have the prismunit, a part of the image erecting means can be shared to the eyepieceoptical system, and space can be effectively utilized. When the eyepieceoptical system is constructed with the unit having a positive refractingpower, the diopter can be adjusted in accordance with the observer'sdiopter.

[0231] In order to keep the size of the finder compact and increase theangle of emergence, it is desirable to reduce the focal length of theeyepiece optical system. Further, in order to reduce the focal length ofthe eyepiece optical system, it is desirable to increase the positiverefracting power of the optical element constituting the eyepieceoptical system.

[0232] However, if the most field-frame-side surface of the eyepieceoptical system is configured so that the positive refracting power isincreased, and a marginal beam in the proximity of the field frame isrendered nearly parallel to the optical axis, the size of the eyepieceoptical system in its radial direction will be increased. On the otherhand, if the most field-frame-side surface of the eyepiece opticalsystem is configured so that the positive refracting power is increased,and at the same time, the size of the eyepiece optical system in itsradial direction is diminished, the angle of inclination will beincreased. Consequently, the marginal beam of the first unit at thewide-angle position is separated from the optical axis, and hence thediameter of the first unit must be enlarged.

[0233] Thus, when the most field-frame-side surface of the eyepieceoptical system has a positive refracting power and is configured as anaspherical surface with a negative refracting power on its periphery,the diameter of the first unit can be diminished. Moreover, correctionfor aberration, notably for distortion, is favorably compatible with apupil combination of the objective optical system and the eyepieceoptical system, notably in an off-axis.

[0234] In the real image mode finder optical system of the presentinvention, it is desirable that the eyepiece optical system includes, inorder from the object side, a prism unit with a positive refractingpower and a lens unit with a positive refracting power so that a mostfield-frame-side surface of the prism unit with a positive refractingpower has a positive refracting power and is configured as an asphericalsurface with a negative refracting power on its periphery.

[0235] As mentioned above, when the eyepiece optical system is designedto have the prism unit, a part of the image erecting means can be sharedto the eyepiece optical system, and space can be effectively utilized.When the eyepiece optical system is constructed with the lens unithaving a positive refracting power, the diopter can be adjusted inaccordance with the observer's diopter.

[0236] In order to reduce the focal length of the eyepiece opticalsystem, it is desirable to increase the positive refracting power of theoptical element constituting the eyepiece optical system.

[0237] However, if the most field-frame-side surface of the eyepieceoptical system is configured so that the positive refracting power isincreased, and a marginal beam in the proximity of the field frame isrendered nearly parallel to the optical axis, the size of the eyepieceoptical system in its radial direction will be increased. On the otherhand, if the most field-frame-side surface of the eyepiece opticalsystem is configured so that the positive refracting power is increased,and at the same time, the size of the eyepiece optical system in itsradial direction is diminished, the angle of inclination will beincreased. Consequently, the marginal beam of the first unit at thewide-angle position is separated from the optical axis, and hence thediameter of the first unit must be enlarged.

[0238] Thus, when the most field-frame-side surface of the eyepieceoptical system has a positive refracting power and is configured as anaspherical surface with a negative refracting power on its periphery,the diameter of the first unit can be diminished. Moreover, correctionfor aberration, notably for distortion, is favorably compatible with apupil combination of the objective optical system and the eyepieceoptical system, notably in an off-axis.

[0239] In the real image mode finder optical system of the presentinvention, it is favorable that the negative refracting power on theperiphery of the most field-frame-side surface of the prism unit with apositive refracting power satisfies the following condition:

−0.7(1/mm)<φ(mh/2)<0(1/mm)  (8)

[0240] where φ(mh/2) is a refracting power at a height mh/2 in adirection normal to the optical axis of the aspherical surface.

[0241] As described above, when Condition (8) is satisfied, the negativerefracting power on the periphery of the most field-frame-side surfaceof the positive prism unit can be optimized.

[0242] Also, a refracting power φ(y) at a height y of the asphericalsurface is obtained as follows. When z is taken as the coordinate in thedirection of the optical axis, y is taken as the coordinate normal tothe optical axis, r denotes the radius of curvature, K denotes a conicconstant, and A₄, A₆, A₈, and A₁₀ denote aspherical coefficients, theconfiguration of the aspherical surface is expressed by the followingequation:

z=(y ² /r)/[1+{square root}{square root over ({1−(1+K)(y/r)²})}]+A ₄ y ⁴+A ₆ y ⁶+A₈ y ⁸ +A ₁₀ y ¹⁰

[0243] Also, first-order differential dz/dy and second-orderdifferential d²z/dy² are given from the following formulas:

dz/dy=(y/r)/[{square root}{square root over ({1−(1+K)(y/r)²})}]+4A ₄ y³+6A ₆ y ⁵+8A ₈ y ⁷+10A ₁₀ y ⁹

d ² z/dy ²=(1/r)/[{1−(1+K)(y/r)²}^(3/2)]+12A ₄ y ²+30A ₆ y ⁴+56A ₈ y⁶+90A ₁₀ y ⁸

[0244] In this case, the refracting power φ(y) at the height y of theaspherical surface is obtained from the following formula:

φ(y)=(n ₂ −n ₁)/r _(asp)

[0245] where n₁ is the refractive index of the aspherical surface on theobject side thereof and n₂ is the refractive index on the image side.

[0246] Also, r_(asp) is defined as

r _(asp)=[{1+(dz/dy)²}^(3/2)]/(d ² z/dy ²)

[0247] It is favorable that the real image mode finder optical system ofthe present invention is constructed so that the objective opticalsystem has at least two lens units, the focal length of the objectiveoptical system is variable, and when the magnification is changed, theat least two lens units are moved along different paths.

[0248] When the objective optical system is constructed so that itsfocal length can be changed, a constant angle of emergence can beobtained, without changing the size of the field frame, even when themagnification is changed.

[0249] When the angle of emergence is increased, the phenomenon of aso-called diopter shift will occur if the back focal position isshifted. However, when at least two lens units are moved along differentpaths to change the magnification, the back focal position of theobjective optical system can be kept to be nearly constant.

[0250] It is favorable that the photographing apparatus according to thepresent invention has the photographing optical system and the realimage mode finder optical system which has been described.

[0251] Also, in the above description, where the reflecting surface isconfigured as a roof reflecting surface, it is assumed that the roofreflecting surface is constructed with two reflecting surfaces.

[0252] The real image mode finder optical system according to thepresent invention includes, in order from the object side, an objectiveoptical system which has a positive refracting power and changes themagnification of the finder, a field frame located in the proximity ofthe imaging position of the objective optical system, and an eyepieceoptical system with a positive refracting power. The real image modefinder optical system has an image erecting means, and the objectiveoptical system includes, in order from the object side, a front unitwith a negative refracting power and a rear unit with a positiverefracting power. The front unit is constructed with a plurality of lensunits so that the magnification is changed, ranging from the wide-angleposition to the telephoto position, by moving at least two of theplurality of lens units. The rear unit is constructed with a pluralityof prism units with positive refracting powers so that at least one ofsurfaces opposite to one another, of the plurality of prism units isconfigured to be convex.

[0253] The real image mode finder optical system according to thepresent invention includes, in order from the object side, an objectiveoptical system which has a positive refracting power and changes themagnification of the finder, a field frame located in the proximity ofthe imaging position of the objective optical system, and an eyepieceoptical system with a positive refracting power. The real image modefinder optical system has an image erecting means, and the objectiveoptical system includes, in order from the object side, a first unitwith a negative refracting power, a second unit with a positiverefracting power, a third unit with a negative refracting power, and afourth unit with a positive refracting power. The fourth unit iscomprised of a fourth front sub-unit with a positive refracting powerand a fourth rear sub-unit with a positive refracting power, and themagnification is changed, ranging from the wide-angle position to thetelephoto position, by moving the second unit and the third unit. Eachof the first, second, and third units is constructed with a lens, andeach of the fourth front and rear sub-units is constructed with a prismso that at least one of surfaces opposite to each other, of the fourthfront and rear sub-units is configured to be convex.

[0254] In the above construction, the real image mode finder opticalsystem is such that the fourth front sub-unit is comprised of a singleprism and has a single reflecting surface.

[0255] In order to increase the angle of emergence, it is only necessaryto increase the size of an image obtained by the objective opticalsystem, that is, the size of the field frame, or to reduce the focallength of the eyepiece optical system. However, if the field frame isenlarged with respect to the focal length of the eyepiece opticalsystem, the objective optical system must be also enlarged. Moreover,since the burden of correction for aberration to the eyepiece opticalsystem will be increased, it becomes difficult that good performance ofthe eyepiece optical system and compactness due to a simple arrangementare compatible with each other. Thus, in order to keep the size of thefinder compact and increase the angle of emergence, it is desirable toreduce the focal length of the eyepiece optical system.

[0256] However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed, so that the reflecting surface to be placedis limited to one. Consequently, it is necessary that the back focaldistance of the objective optical system is increased to place the imageerecting means there.

[0257] Thus, in the present invention, the objective optical system isdesigned to have, in order to the object side, a front unit with anegative refracting power, including a plurality of lens units andchanging the magnification by moving at least two lens units thereof anda rear unit with a positive refracting power comprised of a plurality ofprism units with positive refracting powers.

[0258] As mentioned above, when the objective optical system is designedto be of a retrofocus type, the back focal distance of the objectiveoptical system can be increased. Moreover, when the rear unit with apositive refracting power is constructed with the prism units, the imageerecting means can be shared. Thus, according to the present invention,the focal length of the eyepiece optical system can be reduced, and areal image mode finder optical system which has a large angle ofemergence and is compact in design can be achieved.

[0259] In the case where the variable magnification ratio of the finderoptical system is increased to particularly extend the variablemagnification range to the wide-angle side, a high refracting power isrequired for the rear unit with a positive refracting power. Theinclination of the marginal beam with respect to the optical axis wherethe magnification is changed at the wide-angle position is largeimmediately after the beam emerges from the front unit with a negativerefracting power. Hence, in order to make this inclined beam parallel inthe proximity of the field frame, a great positive refracting power isrequired on the rear side of the front unit with a negative refractingpower. In this case, it is desirable that the great positive refractingpower is shared among a plurality of surfaces because the performance ofthe objective optical system is improved.

[0260] The rear unit with a positive refracting power comprised of aplurality of prism units with positive refracting powers is placed onthe eyepiece side of the front unit with a negative refracting power,and at least one of surfaces opposite to one another, of the pluralityof prism units with positive refracting powers is configured to beconvex. By doing so, the positive refracting power can be shared to theentrance or exit surface of each of the plurality of prism units withpositive refracting powers, and thus the performance of the objectiveoptical system can be improved.

[0261] When the magnification is changed by moving at least two lensunits, the variable magnification function and the diopter correctingfunction involved in the magnification change can be exercised.

[0262] When the angle of emergence is increased, the diopter shift isliable to occur. However, by moving at least two lens units of the frontunit, the diopter shift involved in the magnification change can becorrected.

[0263] As mentioned above, in order to increase the angle of emergence,it is only necessary to increase the size of an image obtained by theobjective optical system, that is, the size of the field frame, or toreduce the focal length of the eyepiece optical system. However, if thefield frame is enlarged with respect to the focal length of the eyepieceoptical system, the objective optical system must be also enlarged.Moreover, since the burden of correction for aberration to the eyepieceoptical system will be increased, it becomes difficult that goodperformance of the eyepiece optical system and compactness due to asimple arrangement are compatible with each other. Thus, in order tokeep the size of the finder compact and increase the angle of emergence,it is desirable to reduce the focal length of the eyepiece opticalsystem.

[0264] However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed, so that the reflecting surface to be placedis limited to one. Consequently, it is necessary that the back focaldistance of the objective optical system is increased to place the imageerecting means there.

[0265] Thus, in the present invention, the objective optical system isdesigned to have, in order to the object side, the first unit with anegative refracting power, the second unit with a positive refractingpower, the third unit with a negative refracting power, and the fourthunit with a positive refracting power so that the fourth unit includesthe fourth front sub-unit with a positive refracting power and thefourth rear sub-unit with a positive refracting power.

[0266] As described above, when the positive refracting power isimparted to each of the fourth front sub-unit and the fourth rearsub-unit, the back focal distance of the objective optical system can beincreased. Moreover, when the fourth front and rear subunits areconstructed with prisms, the function of the image erecting means can beshared. Thus, according to the present invention, the focal length ofthe eyepiece optical system can be reduced, and a real image mode finderoptical system which has a large angle of emergence and is compact indesign can be obtained.

[0267] In the case where In the case where the variable magnificationratio of the finder optical system is increased to particularly extendthe variable magnification range to the wide-angle side, high refractingpowers are required for the units with positive refracting powers on theeyepiece side of the third unit. The inclination of the marginal beamwith respect to the optical axis where the magnification is changed atthe wide-angle position is large immediately after the beam emerges fromthe front unit with a negative refracting power. Hence, in order to makethis inclined beam parallel in the proximity of the field frame, a greatpositive refracting power is required on the rear side of the front unitwith a negative refracting power. In this case, it is desirable that thegreat positive refracting power is shared among a plurality of surfacesbecause the performance of the objective optical system is improved.

[0268] When the prism units of the fourth front and rear sub-units withtwo positive refracting powers are arranged on the eyepiece side of thethird unit and at least one of opposite surfaces of the fourth front andrear sub-units is configured to be convex, the positive refracting powercan be shared to at least one of opposite surfaces of the fourth frontand rear sub-units, and hence the performance of the objective opticalsystem can be improved.

[0269] When the magnification is changed by moving at least two units,the variable magnification function and the diopter correcting functioninvolved in the magnification change can be exercised.

[0270] When the angle of emergence is increased, the diopter shift isliable to occur. However, by moving the second and third units, thediopter shift involved in the magnification change can be corrected.

[0271] In order that the thickness of a camera is reduced to provide acompact camera, it is desirable that a position where the mostobject-side optical axis of the image erecting means, that is, theposition of a reflecting surface, is brought close to the object side.When the magnification is changed, the image erecting means remainsfixed and thereby the arrangement of the finder is simplified. Thus, itis desirable that the fourth front sub-unit with a positive refractingpower has a reflecting surface.

[0272] On the other hand, in order to increase the back focal distanceof the objective optical system, it is desired that most of thereflecting surfaces having positive refracting powers shared between thefourth front and rear sub-units are arranged together at a distance awayfrom the field frame.

[0273] When the objective optical system is constructed so that thefourth front sub-unit has a single reflecting surface as mentionedabove, the opposite surfaces of the fourth front and rear sub-units canbe arranged along the length of the fourth front sub-unit including onereflecting surface. Consequently, compactness of the camera and the backfocal distance of the objective optical system can be ensured.

[0274] In the real image mode finder optical system of the presentinvention, it is favorable that the fourth rear sub-unit is constructedwith a single prism and has two reflecting surfaces.

[0275] At least four reflecting surfaces are required for the imageerecting means, and thus if the image erecting means is constructed withfour reflecting surfaces, space efficiency can be improved. In thiscase, when three of four reflecting surfaces constituting the imageerecting means are placed in the objective optical system, the burden ofa space for placing the image erecting means to the eyepiece opticalsystem is lessened, and the number of optical elements constituting theeyepiece optical system can be reduced.

[0276] It is favorable that the real image mode finder optical system ofthe present invention satisfies the following condition:

−1.0<MG45<−0.5  (9)

[0277] where MG45 is a combined imaging magnification of the fourthfront sub-unit and a fourth rear sub-unit at an object distance of 3 m.

[0278] When Condition (9) is satisfied, the balance between performanceand size of the objective optical system can be held. Below the lowerlimit of Condition (9), a combined refracting power of the first,second, and third units must be increased, and thus the fluctuation ofaberration becomes heavy by movement of the second and third units forchanging the magnification. On the other hand, beyond the upper limit ofCondition (9), a combined refracting power of the first, second, andthird units must be reduced, and thus the diameter of the first unitwill be particularly enlarged.

[0279] When the magnification is changed over the range from thewide-angle position to the telephoto position, it is favorable that thereal image mode finder optical system satisfies the following condition:

−1.2<β3<−0.8  (10)

[0280] where β3 is the imaging magnification of the third unit in astate where the imaging magnification of the second unit is −1× at anobject distance of 3 m.

[0281] The second and third units bear the variable magnificationfunction and the diopter correcting function, but if the dioptercorrection is not completely made, the diopter shift will be produced.In particular, when the angle of emergence is increased, the dioptershift is liable to occur.

[0282] When the finder optical system is designed to satisfy Condition(10), a state where the imaging magnification of the second unit is −1×at an object distance of 3 m practically coincides with a state wherethe imaging magnification of the third unit is −1× at an object distanceof 3 m when the magnification is changed over the range from thewide-angle position to the telephoto position. As a result, dioptercorrection can be favorably made over the whole range in which themagnification is changed.

[0283] In the real image mode finder optical system of the presentinvention, it is favorable that the second unit is constructed with asingle lens and satisfies the following condition:

−0.6<SF2<0.6  (11)

[0284] where SF2=(r3+r4)/(r3−r4), which is the shape factor of thesecond unit, r3 is the radius of curvature of the object-side surface ofthe second unit, and r4 is the radius of curvature of the eyepiece-sidesurface of the second unit.

[0285] When the finder optical system is designed to satisfy Condition(11), the fluctuation of performance where the magnification is changedcan be suppressed. If the upper or lower limit of Condition (11) ispassed, the fluctuation of aberration where the magnification is changedbecomes heavy.

[0286] In the real image mode finder optical system of the presentinvention, it is desirable that each of the second and third units isconstructed with a single lens and satisfies the following condition:

−1.9<f2/f3<−1.0  (12)

[0287] where f2 is the focal length of the second unit and f3 is thefocal length of the third unit.

[0288] Condition (12) defines a condition relative to the refractingpowers of the second and third units for suppressing a change inperformance where the magnification is changed. Below the lower limit ofCondition (12), the refracting power of the third unit is increased, andthe fluctuation of aberration where the magnification is changed becomesheavy. Beyond the upper limit of Condition (12), the refracting power ofthe second unit is increased, and the fluctuation of aberration wherethe magnification is changed becomes heavy.

[0289] It is favorable that the real image mode finder optical system ofthe present invention satisfies the following conditions at the sametime:

−1.0<fw/fFw<−0.4  (13)

−1.0−fT/fFT<−0.4  (14)

[0290] where fFw is a combined focal length of the front unit with anegative refracting power at the wide-angle position, fFT is a combinedfocal length of the front unit with a negative refracting power at thetelephoto position, fw is the focal length of the objective opticalsystem at the wide-angle position, and fT is the focal length of theobjective optical system at the telephoto position.

[0291] When Conditions (13) and (14) are satisfied at the same time, thebalance between the performance and the back focal distance of theobjective optical system can be maintained. If the lower limit ofCondition (13) or (14) is passed, a negative combined refracting powerof the front unit will be strengthened, and thus the fluctuation ofaberration caused by the movement of the second and third units forchanging the magnification becomes heavy.

[0292] On the other hand, if the upper limit of Condition (13) or (14)is exceeded, the negative combined refracting power of the front unitwill be diminished, and hence a long back focal distance caused by theretrofocus arrangement will cease to be completely obtainable.

[0293] It is desirable that the real image mode finder optical system ofthe present invention satisfies the following condition:

2.7<mT/mW<7.0  (15)

[0294] where mW is the finder magnification of the entire system at thewide-angle position and mT is the finder magnification of the entiresystem at the telephoto position.

[0295] The present invention provides a preferred zoom ratio in the realimage mode finder optical system described above.

[0296] Below the lower limit of Condition (15), the performance of thefinder optical system cannot be completely exercised. On the other hand,beyond the upper limit of Condition (15), the refracting power of eachunit becomes too strong and aberration is liable to occur.

[0297] It is favorable that that the photographing apparatus accordingto the present invention has the photographing optical system and thereal image mode finder optical system which has been described.

[0298] Also, in the above description, where the reflecting surface isconfigured as a roof reflecting surface, it is assumed that the roofreflecting surface is constructed with two reflecting surfaces.

[0299] The real image mode finder optical system according to thepresent invention includes, in order from the object side, an objectiveoptical system which has a positive refracting power and changes themagnification of the finder, a field frame located in the proximity ofthe imaging position of the objective optical system, and an eyepieceoptical system with a positive refracting power. The real image modefinder optical system has an image erecting means, and the objectiveoptical system includes, in order from the object side, a first unitwith a negative refracting power, a second unit with a positiverefracting power, a third unit with a negative refracting power, and afourth unit with a positive refracting power. The magnification ischanged, ranging from the wide-angle position to the telephoto position,by simply moving the second unit toward the object side and the thirdunit toward the eyepiece side. A combined focal length of the first,second, and third units is negative, and when the magnification ischanged over the range from the wide-angle position to the telephotoposition, a combined imaging magnification of the second and third unitsis 1×.

[0300] In this case, it is favorable that the real image mode finderoptical system constructed as mentioned above satisfies Condition (10).

[0301] Furthermore, in the real image mode finder optical system of thepresent invention, it is favorable that the second unit is constructedwith a single lens and satisfies Condition (11).

[0302] As described above, in order to increase the angle of emergence,it is only necessary to increase the size of an image obtained by theobjective optical system, that is, the size of the field frame, or toreduce the focal length of the eyepiece optical system. However, if thefield frame is enlarged with respect to the focal length of the eyepieceoptical system, the objective optical system must be also enlarged.Moreover, since the burden of correction for aberration to the eyepieceoptical system will be increased, it becomes difficult that goodperformance of the eyepiece optical system and compactness due to asimple arrangement are compatible with each other. Thus, in order tokeep the size of the finder compact and increase the angle of emergence,it is desirable to reduce the focal length of the eyepiece opticalsystem.

[0303] However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed. Consequently, it is necessary that the backfocal distance of the objective optical system is increased to place theimage erecting means there.

[0304] Thus, in the present invention, the objective optical system isdesigned to have, in order to the object side, the first unit with anegative refracting power, the second unit with a positive refractingpower, the third unit with a negative refracting power, and the fourthunit with a positive refracting power so that the combined focal lengthof the first, second, and third units is negative.

[0305] By doing so, the objective optical system is arranged to be of aretrofocus type, and therefore, the back focal distance of the objectiveoptical system can be increased.

[0306] Thus, according to the present invention, the focal length of theeyepiece optical system can be reduced, and a real image mode finderoptical system which has a large angle of emergence and is compact indesign can be achieved.

[0307] When the magnification of the finder is changed, it is necessarythat a variable magnification function is chiefly imparted to one of atleast two moving lens units and a diopter correcting function involvedin the magnification change is chiefly imparted to the other. In thiscase, the amount of movement of the lens unit having the variablemagnification function becomes larger than that of the lens unit havingthe diopter correcting function, and a mechanism for movement is liableto be complicated and oversized.

[0308] Thus, in the present invention, the finder optical system isconstructed so that the magnification is changed, ranging from thewide-angle position to the telephoto position, by simply moving thesecond unit toward the object side and the third unit toward theeyepiece side.

[0309] By doing so, both the variable magnification function and thediopter correcting function can be shared between the second unit andthe third unit. Hence, the amount of movement of each of the second andthird units where the magnification is change can be kept to a minimum,and compactness of the mechanism for movement is obtained.

[0310] In order to achieve compactness of the objective optical system,it is only necessary to increase the refracting power of each of thesecond and third units for changing the magnification. In this case,however, the fluctuation of aberration where the magnification ischanged becomes heavy.

[0311] Here, in the whole range in which the magnification is changed,if an attempt is made so that the combined imaging magnification of thesecond and third units becomes lower than 1×, there is a tendency thatthe refracting power of the third unit is increased. In this case, sincethe refracting power of the first unit must be diminished, the diameterof the first unit must be increased.

[0312] On the other hand, if an attempt is made so that the combinedimaging magnification of the second and third units becomes higher than1×, there is a tendency that the refracting power of the second unit isincreased. In this case, since the refracting power of the first unitmust be increased, the diopter shift caused by a change of space betweenthe first and second units becomes particularly considerable.

[0313] Thus, if the combined imaging magnification of the second andthird units is changed so that it becomes 1×, the balance between theperformance and the size of the objective optical system can beoptimized.

[0314] The second and third units bear the variable magnificationfunction and the diopter correcting function, but if the dioptercorrection is not completely made, the diopter shift will be produced.In particular, when the angle of emergence is increased, the dioptershift is liable to occur.

[0315] When the finder optical system is designed to satisfy Condition(10), a state where the imaging magnification of the second unit is −1×at an object distance of 3 m practically coincides with a state wherethe imaging magnification of the third unit is −1× at an object distanceof 3 m when the magnification is changed over the range from thewide-angle position to the telephoto position. As a result, dioptercorrection can be favorably made over the whole range in which themagnification is changed.

[0316] When the finder optical system is designed to satisfy Condition(11), the fluctuation of performance where the magnification is changedcan be suppressed. If the upper or lower limit of Condition (11) ispassed, the fluctuation of aberration where the magnification is changedbecomes heavy.

[0317] In the real image mode finder optical system of the presentinvention, it is favorable that each of the second and third units isconstructed with a single lens and satisfies Condition (12).

[0318] Condition (12) defines a condition relative to the refractingpowers of the second and third units for suppressing a change inperformance where the magnification is changed. Below the lower limit ofCondition (12), the refracting power of the third unit is increased, andthe fluctuation of aberration where the magnification is changed becomesheavy. Beyond the upper limit of Condition (12), the refracting power ofthe second unit is increased, and the fluctuation of aberration wherethe magnification is changed becomes heavy.

[0319] It is favorable that the real image mode finder optical system ofthe present invention satisfies the following conditions at the sametime:

−1.0<fw/fw123<−0.4  (16)

−1.0<fr/fr123<−0.4  (17)

[0320] where fw123 is a combined focal length of the first, second, andthird units at the wide-angle position and fT123 is a combined focallength of the first, second, and third units at the telephoto position.

[0321] When Conditions (16) and (17) are satisfied at the same time, thebalance between the performance and the back focal distance of theobjective optical system can be maintained. If the lower limit ofCondition (16) or (17) is passed, a negative combined refracting powerof each of the first, second, and third units will be strengthened, andthus the fluctuation of aberration caused by the movement of the secondand third units for changing the magnification becomes heavy.

[0322] On the other hand, if the upper limit of Condition (16) or (17)is exceeded, the negative combined refracting power of each of thefirst, second, and third units will be diminished, and hence a long backfocal distance caused by the retrofocus arrangement will cease to becompletely obtainable.

[0323] It is favorable that the real image mode finder optical system isconstructed so that when the magnification is changed over the rangefrom the wide-angle position to the telephoto position, the fourth unitremains fixed.

[0324] By doing so, the number of units to be moved can be lessened, andcost can be reduced accordingly.

[0325] In the real image mode finder optical system of the presentinvention, it is favorable that the fourth unit is constructed with twooptical units with positive refracting powers.

[0326] In the case where the variable magnification ratio of the finderoptical system is increased to particularly extend the variablemagnification range to the wide-angle side, a high refracting power isrequired for the unit with a positive refracting power on the eyepieceside of the third unit. The inclination of the marginal beam withrespect to the optical axis where the magnification is changed at thewide-angle position is large immediately after the beam emerges from thethird unit. Hence, in order to make this inclined beam parallel in theproximity of the field frame, a great positive refracting power isrequired on the rear side of the third unit. In this case, it isdesirable that the great positive refracting power is shared among aplurality of surfaces because the performance of the objective opticalsystem is improved.

[0327] As explained above, when the two optical units with positiverefracting powers are arranged on the eyepiece side of the third unit,the lens function can be shared between opposite surfaces of the twooptical units with positive refracting powers, and hence the performanceof the objective optical system can be improved.

[0328] In the real image mode finder optical system of the presentinvention, it is favorable that the fourth unit has a plurality ofreflecting surfaces.

[0329] Thus, when at least half of the image erecting function is sharedto the objective optical system, an increase in thickness along theoptical axis of incidence of the objective optical system can besuppressed and at the same time, the distance between an intermediateimage and an eyepiece is reduced. Consequently, a finder which has alarge angle of emergence can be obtained.

[0330] In the real image mode finder optical system of the presentinvention, it is favorable that the two optical units are prisms havingreflecting surfaces.

[0331] When at least half of the image erecting function is shared tothe objective optical system, an increase in thickness along the opticalaxis of incidence of the objective optical system can be suppressed andat the same time, the distance between an intermediate image and aneyepiece is reduced. Consequently, a finder which has a large angle ofemergence can be obtained.

[0332] It is favorable that the real image mode finder optical system isconstructed so that the magnification is changed, ranging from thewide-angle position to the telephoto position, by moving the first unitas well.

[0333] The second and third units bear the variable magnificationfunction and the diopter correcting function, but if the dioptercorrection is not completely made, the diopter shift will be produced.

[0334] Where the units for changing the magnification are constructedwith only the second and third units, diopter correction cannot befavorably made over the whole range in which the magnification ischanged, unless a state where the imaging magnification of the secondunit is −1× practically coincides with a state where the imagingmagnification of the third unit is −1× when the magnification is changedover the range from the wide-angle position to the telephoto position.

[0335] However, when the first unit is also moved to change themagnification, restrictions on imaging magnifications of the second andthird units are eliminated, and the performance of the objective opticalsystem can be easily improved.

[0336] The real image mode finder optical system of the presentinvention may be constructed so that when the magnification is changedover the range from the wide-angle position to the telephoto position,the first unit remains fixed.

[0337] By doing so, the number of units to be moved can be lessened, andcost can be reduced accordingly.

[0338] In this case, it is favorable that the real image mode finderoptical system of the present invention satisfies Condition (15).

[0339] The present invention provides a preferred zoom ratio in the realimage mode finder optical system described above.

[0340] Below the lower limit of Condition (15), the performance of thefinder optical system cannot be completely exercised. On the other hand,beyond the upper limit of Condition (15), the refracting power of eachunit becomes too strong and aberration is liable to occur.

[0341] It is favorable that that the photographing apparatus accordingto the present invention has the photographing optical system and thereal image mode finder optical system which has been described.

[0342] Also, in the above description, where the reflecting surface isconfigured as a roof reflecting surface, it is assumed that the roofreflecting surface is constructed with two reflecting surfaces.

[0343] In accordance with the drawings and numerical data, theembodiments of the real image mode finder optical system of the presentinvention will be explained below.

[0344] In any of the embodiments, the real image mode finder opticalsystem includes, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame placed in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power, and has animage erecting means.

[0345] First Embodiment

[0346] In the real image mode finder optical system of this embodiment,as shown in FIGS. 1-3 and 5A-5C, the objective optical system includes,in order from the object side, a first unit G1 with a negativerefracting power, a second unit G2 with a positive refracting power, athird unit G3 with a negative refracting power, and a fourth unit G4with a positive refracting power, and has a positive refracting power asa whole.

[0347] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with a prism P and a positivelens E1 and has a positive refracting power as a whole. Also, in FIG.5A, symbol EP represents an eyepoint.

[0348] The image erecting means includes the prisms P1 and P2 and theprism P. In the real image mode finder optical system of the firstembodiment, an intermediate image formed by the objective optical systemis interposed between the prism P2 and the prism P, and the field frame,such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

[0349] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by moving the second unit G2 and the thirdunit G3 along the optical axis.

[0350] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havefinite curvatures. The entrance surface and the exit surface of theprism P also have finite curvatures.

[0351] The prisms P1 and P2 and the prism P, as shown in FIGS. 1-3, areprovided with reflecting surfaces P1 ₁, P2 ₁, P2 ₂, and P₁ along theoptical path so that the optical axis is bent to erect an image.Specifically, as shown in FIG. 3, the reflecting surface P1 ₁ providedin the prism P1 bends the optical axis in a Y-Z plane; as shown in FIGS.2 and 3, the two reflecting surfaces P2 ₁ and P2 ₂ provided in the prismP2 bend the optical axis in the Y-Z plane and an X-Z plane in this orderfrom the object side; and as shown in FIG. 2, the reflecting surface P₁provided in the prism P bends the optical axis in the X-Z plane. In thisway, an erect image is obtained. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangles of the optical axis bent by the reflecting surfaces P1 ₁ and P₁of the prism P1 and the prism P are smaller than 90 degrees and theangles of the optical axis bent by the reflecting surfaces P2 ₁ and P2 ₂of the prism P2 are larger than 90 degrees. The reflecting surfaces P1 ₁and P₁ of the prism P1 and the prism P are coated with metal films, suchas silver and aluminum. The reflecting surfaces P2 ₁ and P2 ₂ of theprism P2 utilize total reflection.

[0352] However, the ways of bending the optical axis through the prismsand the angles of the optical axis bent by the reflecting surfaces arenot limited to the above description. For example, the angle of theoptical axis bent by the most field-frame-side reflecting surface P2 ₂of the prism P2 may be made smaller than 90 degrees so that thisreflecting surface is coated with a metal film. Moreover, the angle ofthe optical axis bent by the reflecting surface P₁ of the prism P mayalso be made larger than 90 degrees so that this reflecting surfaceutilizes total reflection.

[0353] The positive lens E1 is constructed so that diopter adjustmentcan be made in accordance with an observer's diopter.

[0354] Also, aberration characteristics in the first embodiment areshown in FIGS. 6A-6D, 7A-7D, and 8A-8D.

[0355] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the first embodimentare shown below. In the numerical data of the first embodiment, mdenotes a finder magnification; ω denotes a field angle; f denotes thefocal length of the objective optical system; r₁, r₂, represent radii ofcurvature of the surfaces of individual lenses or prisms; d₁, d₂,represent thicknesses of individual lenses or prisms or spacestherebetween; n_(d1), n_(d2), represent refractive indices of individuallenses or prisms; and v_(d1), v_(d2), . . . represent Abbe's numbers ofindividual lenses or prisms; mh represents the maximum width of thefield frame; fe represents the focal length of the eyepiece opticalsystem; f123 represents a combined focal length of the first to thirdunits; m23 represents a combined imaging magnification of the second andthird units where an object distance is 3 m; m2 represents an imagingmagnification of the second unit at the middle position where the objectdistance is 3 m; and m3 represents an imaging magnification of the thirdunit at the middle position where the object distance is 3 m.

[0356] Also, the configuration of the aspherical surface, as alreadydescribed, is expressed by the following equation:

z=(y ² /r)/[1+{square root}{square root over ({1−(1+K)(y/r)²})}]+A ₄ y ⁴+A ₆ y ⁶ +A ₈ y ⁸ +A ₁₀ y ¹⁰

[0357] These symbols are also applied to the embodiments to be describedlater.

[0358] Numerical Data 1 Wide-angle position Middle position Telephotoposition m  0.536  1.016  2.075 ω (°) 33.541 17.525  8.746 f (mm)  8.04715.253 31.147 Pupil dia. (mm)  4.000 r₁ = 83.6172 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 10.0913 (aspherical) d₂ = D2 (variable) r₃ =10.3392 (aspherical) d₃ = 4.3149 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−21.0217 (aspherical) d₄ = D2 (variable) r₅ = −10.0239 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3239 (aspherical) d₆ = D6(variable) r₇ = 11.2869 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−23.2085 (aspherical) d₈ = 0.5000 r₉ = 15.7633 (aspherical) d₉ = 22.5495n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.2605 r₁₁ = ∞ (fieldframe) d₁₁ = 2.5500 r₁₂ = 15.9503 (aspherical) d₁₂ = 15.5600 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −38.8890 d₁₃ = 1.7500 r₁₄ = 25.2612 d₁₄ =5.3200 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −16.9795 (aspherical) d₁₅= 17.0491 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2950 A₄ = 2.10279 × 10⁻⁶ A₆ = −2.71836 × 10⁻⁷ A₈ = 1.45499 × 10⁻⁹Third surface K = −0.2610 A₄ = −9.12395 × 10⁻⁵ A₆ = −3.93632 × 10⁻⁷ A₈ =−6.31136 × 10⁻⁹ Fourth surface K = −0.0224 A₄ = 8.97235 × 10⁻⁵ A₆ =−4.73271 × 10⁻⁷ A₈ = −1.37810 × 10⁻⁹ Fifth surface K = 0.2143 A₄ =6.18253 × 10⁻⁴ A₆ = −3.45137 × 10⁻⁵ A₈ = 7.99836 × 10⁻⁷ Sixth surface K= −0.0423 A₄ = 1.66996 × 10⁻⁶ A₆ = −2.60860 × 10⁻⁵ A₈ = 6.01778 × 10⁻⁷Eighth surface K = 0.1568 A₄ = 2.22420 × 10⁻⁴ A₆ = −1.28141 × 10⁻⁶ A₈ =3.95727 × 10⁻⁸ Ninth surface K = 0.0140 A₄ = −1.11940 × 10⁻⁵ A₆ =−1.42736 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Fifteenth surface K = 0.0000 A₄ = 4.29178 × 10⁻⁵ A₆ =1.34232 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2   11.6242    7.1879    3.4246 D4    1.2500    8.2976  16.2705 D6    7.8209    5.2097    1.0000 mh = 10.139 mm f123 −10.436−19.857 −41.578 m23    0.529    1.000    2.044 m2  −1.000 m3  −1.000Condition (9) MG45 −0.773  −0.775  −0.776 Conditions (1), (7) mh/fe =0.676 Conditions (2), (3) fe = 15.009 mm Condition (8) Φ(mh/2) =−0.377955 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.341Condition (12) f2/f3 = −1.619 Condition (13) fw/fFw = −0.771 Condition(14) fT/fFT = −0.749 Condition (15) mT/mW = 3.871 Condition (16)fw/fw123 = −0.771 Condition (17) fT/fT123 = −0.749

[0359] Second Embodiment

[0360] In the real image mode finder optical system of this embodiment,as shown in FIGS. 9A-9C, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and the fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0361] The fourth unit G4 is constructed with a positive lens L and theprism P1. The eyepiece optical system is constructed with a prism P anda positive lens E1 and has a positive refracting power as a whole.

[0362] The image erecting means includes the prism P1 and the prism P.In the real image mode finder optical system of the second embodiment,the intermediate image formed by the objective optical system isinterposed between the prism P1 and the prism P, and the field frame,such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

[0363] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

[0364] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of the prism P1 have finite curvatures. The entrance surface andthe exit surface of the prism P also have finite curvatures.

[0365] The prism P1 and the prism P are provided with reflectingsurfaces along the optical path so that the optical axis is bent toobtain an erect image. For example, the prism P1 is provided with threereflecting surfaces (for bending the optical axis twice in the Y-Z planeand once in the X-Z plane in this order from the object side) and theprism P is provided with one reflecting surface (for bending the opticalaxis in the X-Z plane) to erect the image. Also, the arrangement of thereflecting surfaces is based on that of a Porro prism. Angles made withthe optical axis bent by the reflecting surfaces are such that, forexample, the angle of the optical axis bent by one reflecting surface ofthe prism P1 is smaller than 90 degrees and the angles of the opticalaxis bent by the remaining two reflecting surfaces are larger than 90degrees, while the angle of the optical axis bent by the reflectingsurface of the prism P is smaller than 90 degrees. The reflectingsurfaces making angles smaller than 90 degrees are coated with metalfilms, such as silver and aluminum. The reflecting surfaces of angleslarger than 90 degrees utilize total reflection. However, the angles ofthe optical axis bent by the reflecting surfaces are not limited to theabove description. For example, the angle of the optical axis bent bythe most field-frame-side reflecting surface of the prism P1 may be madesmaller than 90 degrees so that this reflecting surface is coated with ametal film. Moreover, the angle of the optical axis bent by thereflecting surface of the prism P may also be made larger than 90degrees so that this reflecting surface utilizes total reflection.

[0366] The positive lens E1 is constructed so that diopter adjustmentcan be made in accordance with an observer's diopter.

[0367] Also, aberration characteristics in the second embodiment areshown in FIGS. 10A-10D, 11A-11D, and 12A-12D.

[0368] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the second embodimentare shown below.

[0369] Numerical Data 2 Wide-angle position Middle position Telephotoposition m  0.685  1.176  2.016 ω (°) 26.680 15.434  8.985 f (mm) 10.29017.649 30.256 Pupil dia. (mm)  4.000 r₁ = 37.0457 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 9.2320 (aspherical) d₂ = D2 (variable) r₃ =9.5256 (aspherical) d₃ = 4.4760 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ =−22.0049 d₄ = D4 (variable) r₅ = −10.2911 d₅ = 0.7000 n_(d5) = 1.58423ν_(d5) = 30.49 r₆ = 9.8912 (aspherical) d₆ = D6 (variable) r₇ = 36.5176d₇ = 3.5263 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −11.2570 (aspherical)d₈ = 0.5000 r₉ = 17.5358 d₉ = 29.0967 n_(d9) = 1.52542 ν_(d9) = 55.78r₁₀ = −218.6484 d₁₀ = 2.7527 r₁₁ = ∞ (field frame) d₁₁ = 2.9177 r₁₂ =19.1732 (aspherical) d₁₂ = 17.0445 n_(d12) = 1.52542 ν_(d12) = 55.78 r₁₃= −20.5269 d₁₃ = 1.4765 r₁₄ = 39.9369 (aspherical) d₁₄ = 3.4455 n_(d14)= 1.52542 ν_(d14) = 55.78 r₁₅ = −20.1555 (aspherical) d₁₅ = 15.7651 r₁₆= ∞ (eyepoint) Aspherical coefficients Second surface K = −1.3017 A₄ =4.40512 × 10⁻⁵ A₆ = 1.04845 × 10⁻⁶ A₈ = −4.86973 × 10⁻⁹ Third surface K= −0.1847 A₄ = −1.74316 × 10⁻⁴ A₆ = −2.38197 × 10⁻⁷ A₈ = −6.24988 × 10⁻⁹Sixth surface K = −0.0683 A₄ = −4.82178 × 10⁻⁴ A₆ = 3.96724 × 10⁻⁶ A₈ =−3.64804 × 10⁻⁸ Eighth surface K = 0.1808 A₄ = 9.81681 × 10⁻⁵ A₆ =8.46115 × 10⁻⁷ A₈ = 8.50642 × 10⁻⁹ Twelfth surface K = 0.0000 A₄ =−5.68528 × 10⁻⁴ A₆ = −1.76882 × 10⁻⁷ Fourteenth surface K = 0.0000 A₄ =−5.49243 × 10⁻⁵ A₆ = 1.22082 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ =−2.37429 × 10⁻⁵ A₆ = 1.03731 × 10⁻⁶ Wide-angle position Middle positionTelephoto position Zoom data D2 11.6070 8.0586  4.1006 D4  1.1067 7.008613.2454 D6  6.3793 4.0397  1.6737 mh = 9.765 mm Conditions (1), (7)mh/fe = 0.650 Conditions (2), (3) fe = 15.011 mm

[0370] Third Embodiment

[0371] In the real image mode finder optical system of this embodiment,as shown in FIGS. 13A-13C, the objective optical system includes, inorder from the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0372] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with a negative lens L1 and thepositive lens E1 and has a positive refracting power as a whole.

[0373] The image erecting means includes the prisms P1 and P2. In thereal image mode finder optical system of the third embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P2 and the negative lens L1, and the field frame, suchas that shown in FIG. 4, is placed in the proximity of its imagingposition.

[0374] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

[0375] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of each of the prisms P1 and P2 have finite curvatures.

[0376] The prisms P1 and P2 are provided with reflecting surfaces alongthe optical path so that the optical axis is bent to obtain an erectimage. For example, the prism P1 is provided with one reflecting surface(for bending the optical axis in the Y-Z plane) and the prism P2 isprovided with three reflecting surfaces (for bending the optical axisonce in the Y-Z plane and twice in the X-Z plane in this order from theobject side) to erect the image. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangle of the optical axis bent by the reflecting surface of the prism P1is smaller than 90 degrees, while the angles of the optical axis bent bytwo reflecting surfaces of the prism P2 are larger than 90 degrees andthe angle of the optical axis bent by the remaining one reflectingsurface is smaller than 90 degrees. The reflecting surfaces makingangles smaller than 90 degrees are coated with metal films, such assilver and aluminum. The reflecting surfaces of angles larger than 90degrees utilize total reflection. The positive lens E1 is constructed sothat diopter adjustment can be made in accordance with an observer'sdiopter.

[0377] Also, aberration characteristics in the third embodiment areshown in FIGS. 14A-14D, 15A-15D, and 16A-16D.

[0378] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the third embodimentare shown below.

[0379] Numerical Data 3 Wide-angle position Middle position Telephotoposition m  0.692  1.181  2.018 ω (°) 26.656 15.374  8.976 f (mm) 10.37517.709 30.248 Pupil dia. (mm)  4.000 r₁ = −37.0118 d₁ = 1.6264 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 15.0266 (aspherical) d₂ = D2 (variable) r₃ =13.6624 (aspherical) d₃ = 4.2776 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ =−19.7350 d₄ = D4 (variable) r₅ = −23.9768 d₅ = 0.6800 n_(d5) = 1.58423ν_(d5) = 30.49 r₆ = 15.4052 (aspherical) d₆ = D6 (variable) r₇ = 64.0979d₇ = 14.4273 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −16.0524 (aspherical)d₈ = 0.5000 r₉ = 46.4363 d₉ = 39.5267 n_(d9) = 1.52542 ν_(d9) = 55.78r₁₀ = −21.0120 d₁₀ = 3.7943 r₁₁ = ∞ (field frame) d₁₁ = 6.9095 r₁₂ =−9.9877 (asphrical) d₁₂ = 3.6912 n_(d12) = 1.58423 ν_(d12) = 30.49 r₁₃ =−15.7572 d₁₃ = 0.9421 r₁₄ = 19.1293 (aspherical) d₁₄ = 7.8836 n_(d14) =1.52542 ν_(d14) = 55.78 r₁₅ = −10.9574 (aspherical) d₁₅ = 15.7651 r₁₆ =∞ (eyepoint) Aspherical coefficients Second surface K = −1.3019 A₄ =−1.08535 × 10⁻⁴ A₆ = 1.48477 × 10⁻⁶ A₈ = −7.37060 × 10⁻⁹ Third surface K= −0.1784 A₄ = −1.38562 × 10⁻⁴ A₆ = 1.91486 ×10⁻⁷ A₈ = −9.59282 × 10⁻¹⁰Sixth surface K = −0.0760 A₄ = −4.70450 × 10⁻⁵ A₆ = −2.11500 × 10⁻⁶ A₈ =3.61544 × 10⁻⁸ Eighth surface K = 0.1930 A₄ = 4.06798 × 10⁻⁵ A₆ =−8.51164 × 10⁻⁸ A₈ = 3.41981 × 10⁻⁹ Twelfth surface K = 0.0000 A₄ =−4.97284 × 10⁻⁴ A₆ = −5.19125 × 10⁻⁶ Fourteenth surface K = 0.0000 A₄=1.11128 × 10⁻⁴ A₆ = −2.84749 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ =1.70029 × 10⁻⁴ A₆ = −6.56818 × 10⁻⁷ Wide-angle position Middle positionTelephoto position Zoom data D2 25.7084 12.8854  7.7602 D4  1.0000 9.0863 19.8650 D6  2.8644  5.0585  1.4948 mh = 9.621 mm Conditions (1),(7) mh/fe = 0.642 Conditions (2), (3) fe = 14.990 mm

[0380] Fourth Embodiment

[0381] In the real image mode finder optical system of this embodiment,as shown in FIGS. 17A-17C, the objective optical system includes, inorder from the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0382] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the negative lens L1 and thepositive lens E1 and has a positive refracting power as a whole.

[0383] The image erecting means includes the prisms P1 and P2. In thereal image mode finder optical system of the fourth embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P2 and the negative lens L1, and the field frame, suchas that shown in FIG. 4, is placed in the proximity of its imagingposition.

[0384] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

[0385] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of each of the prisms P1 and P2 have finite curvatures.

[0386] The prisms P1 and P2 are provided with reflecting surfaces alongthe optical path so that the optical axis is bent to obtain an erectimage. For example, the prism P1 is provided with one reflecting surface(for bending the optical axis in the Y-Z plane) and the prism P2 isprovided with three reflecting surfaces (for bending the optical axisonce in the Y-Z plane and twice in the X-Z plane in this order from theobject side) to erect the image. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangle of the optical axis bent by the reflecting surface of the prism P1is smaller than 90 degrees, while the angles of the optical axis bent bytwo reflecting surfaces of the prism P2 are larger than 90 degrees andthe angle of the optical axis bent by the remaining one reflectingsurface is smaller than 90 degrees. The reflecting surfaces makingangles smaller than 90 degrees are coated with metal films, such assilver and aluminum. The reflecting surfaces of angles larger than 90degrees utilize total reflection. The positive lens E1 is constructed sothat diopter adjustment can be made in accordance with an observer'sdiopter.

[0387] Also, aberration characteristics in the fourth embodiment areshown in FIGS. 18A-18D, 19A-19D, and 20A-20D.

[0388] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the fourth embodimentare shown below.

[0389] Numerical Data 4 Wide-angle position Middle position Telephotoposition m  0.574  0.980  1.680 ω (°) 26.946 15.541  9.003 f (mm)  8.61214.706 25.218 Pupil dia. (mm)  4.000 r₁ = −27.7265 d₁ = 0.7033 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 12.5528 (aspherical) d₂ = D2 (variable) r₃ =11.3610 (aspherical) d₃ = 3.8444 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ =−15.8341 d₄ = D4 (variable) r₅ = −18.1098 d₅ = 0.7000 n_(d5) = 1.58423ν_(d5) = 30.49 r₆ = 11.6071 (aspherical) d₆ = D6 (variable) r₇ = 53.8289d₇ = 12.8726 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −14.5655 (aspherical)d₈ = 1.0000 r₉ = 23.4433 d₉ = 34.8807 n_(d9) = 1.52542 ν_(d9) = 55.78r₁₀ = −28.7418 d₁₀ = 1.4329 r₁₁ = ∞ (field frame) d₁₁ = 6.9526 r₁₂ =−12.6182 (aspherical) d₁₂ = 3.6221 n_(d12) = 1.58423 ν_(d12) = 30.49 r₁₃= −15.2579 d₁₃ = 1.1803 r₁₄ = 24.0716 (aspherical) d₁₄ = 8.3376 n_(d14)= 1.52542 ν_(d14) = 55.78 r₁₅ = −11.3348 (aspherical) d₁₅ = 15.7651 r₁₆= ∞ (eyepoint) Aspherical coefficients Second surface K = −1.3022 A₄ =−2.00833 × 10⁻⁴ A₆ = 3.41784 × 10⁻⁶ A₈ = −1.63261 × 10⁻⁸ Third surface K= −0.1825 A₄ = −2.54261 × 10⁻⁴ A₆ = 5.60513 × 10⁻⁷ A₈ = −3.79136 × 10⁻⁹Sixth surface K = −0.0762 A₄ = −1.57743 × 10⁻⁴ A₆ = −3.09431 × 10⁻⁶ A₈ =4.76542 × 10⁻⁸ Eighth surface K = 0.1928 A₄ = 4.63808 × 10⁻⁵ A₆ =−2.97595 × 10⁻⁷ A₈ = 8.60163 × 10⁻⁹ Twelfth surface K = 0.0000 A₄ =−6.08556 × 10⁻⁴ A₆ = −8.85765 × 10⁻⁶ Fourteenth surface K = 0.0000 A₄ =1.52011 × 10⁻⁴ A₆ = −1.19503 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ =1.06106 × 10⁻⁴ A₆ = 8.55846 × 10⁻⁷ Wide-angle position Middle positionTelephoto position Zoom data D2 21.4497 10.4751  6.4304 D4  1.0000 7.7777 16.8353 D6  1.9906  3.8269  1.3800 mh = 8.107 mm Conditions (1),(7) mh/fe = 0.540 Conditions (2), (3) fe = 15.010 mm

[0390] Fifth Embodiment

[0391] In the real image mode finder optical system of this embodiment,as shown in FIGS. 21A-21C, the objective optical system includes, inorder from the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0392] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the negative lens L1 and thepositive lens E1 and has a positive refracting power as a whole.

[0393] The image erecting means includes the prisms P1 and P2. In thereal image mode finder optical system of the fifth embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P2 and the negative lens L1, and the field frame, suchas that shown in FIG. 4, is placed in the proximity of its imagingposition.

[0394] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

[0395] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of each of the prisms P1 and P2 have finite curvatures.

[0396] The prisms P1 and P2 are provided with reflecting surfaces alongthe optical path so that the optical axis is bent to obtain an erectimage. For example, the prism P1 is provided with one reflecting surface(for bending the optical axis in the Y-Z plane) and the prism P2 isprovided with three reflecting surfaces (for bending the optical axisonce in the Y-Z plane and twice in the X-Z plane in this order from theobject side) to erect the image. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangle of the optical axis bent by the reflecting surface of the prism P1is smaller than 90 degrees, while the angles of the optical axis bent bytwo reflecting surfaces of the prism P2 are larger than 90 degrees andthe angle of the optical axis bent by the remaining one reflectingsurface is smaller than 90 degrees. The reflecting surfaces makingangles smaller than 90 degrees are coated with metal films, such assilver and aluminum. The reflecting surfaces of angles larger than 90degrees utilize total reflection. The positive lens E1 is constructed sothat diopter adjustment can be made in accordance with an observer'sdiopter.

[0397] Also, aberration characteristics in the fifth embodiment areshown in FIGS. 22A-22D, 23A-23D, and 24A-24D.

[0398] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the fifth embodimentare shown below.

[0399] Numerical Data 5 Wide-angle position Middle position Telephotoposition m  0.873  1.293  2.418 ω (°) 24.751 16.220  8.611 f (mm) 13.11019.409 36.290 Pupil dia. (mm)  4.000 r₁ = −39.3543 d₁ = 2.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 20.1886 (aspherical) d₂ = D2 (variable) r₃ =17.8228 (aspherical) d₃ = 4.5550 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ =−20.6969 d₄ = D4 (variable) r₅ = −26.5948 d₅ = 0.9712 n_(d5) = 1.58423V_(d5) = 30.49 r₆ = 21.3842 (aspherical) d₆ = D6 (variable) r₇ = 49.7469d₇ = 16.0933 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −23.8038 (aspherical)d₈ = 0.6446 r₉ = 38.3198 d₉ = 43.7612 n_(d9) = 1.52542 ν_(d9) = 55.78r₁₀ = −63.9202 d₁₀ = 2.7501 r₁₁ = ∞ (field frame) d₁₁ = 7.1509 r₁₂ =−7.9810 (aspherical) d₁₂ = 3.6432 n_(d12) = 1.58423 ν_(d12) = 30.49 r₁₃= −11.3215 d₁₃ = 1.2765 r₁₄ = 16.6904 (aspherical) d₁₄ = 7.6344 n_(d14)= 1.52542 ν_(d14) = 55.78 r₁₅ = −13.2210 (aspherical) d₁₅ = 15.7651 r₁₆= ∞ (eyepoint) Aspherical coefficients Second surface K = −1.3021 A₄ =−3.80325 × 10⁻⁵ A₆ = 5.97449 × 10⁻⁷ A₈ = −2.67271 × 10⁻⁹ Third surface K= −0.1774 A₄ = −7.61365 × 10⁻⁵ A₆ = 1.22273 × 10⁻⁷ A₈ = −3.41547 × 10⁻¹⁰Sixth surface K = −0.0759 A₄ = −3.60399 × 10⁻⁵ A₆ = −1.18573 × 10⁻⁷ A₈ =9.28811 × 10⁻¹⁰ Eighth surface K = 0.1900 A₄ = 1.33964 × 10⁻⁵ A₆ =5.39206 × 10⁻⁸ A₈ = −9.03386 × 10⁻¹¹ Twelfth surface K = 0.0000 A₄ =−2.69230 × 10⁻⁴ A₆ = −2.03083 × 10⁻⁶ Fourteenth surface K = 0.0000 A₄ =8.14903 × 10⁻⁵ A₆ = −1.34641 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ =1.81061 × 10⁻⁴ A₆ = −6.24901 × 10⁻⁷ Wide-angle position Middle positionTelephoto position Zoom data D2 29.0804 15.7590  8.2552 D4  1.0000 8.0891 22.1773 D6  3.1755  8.1368  2.0110 mh = 11.006 mm Conditions(1), (7) mh/fe = 0.733 Conditions (2), (3) fe = 15.010 mm

[0400] Sixth Embodiment

[0401] The arrangement of this embodiment is similar to that of thefirst embodiment described with reference to FIGS. 1-4. FIGS. 25A-25Dshow the arrangement of the sixth embodiment. In this embodiment,low-dispersion glass is used for the positive lens E1 to suppresschromatic aberration of magnification produced in the eyepiece opticalsystem.

[0402] Also, aberration characteristics in the sixth embodiment areshown in FIGS. 26A-26D, 27A-27D, 28A-28D, and 29A-29D.

[0403] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the sixth embodimentare shown below.

[0404] Numerical Data 6 Wide-angle position Middle position Telephotoposition m  0.743  1.016  2.072 ω (°) 23.854 17.511  8.739 f (mm) 11.15615.252 31.104 Pupil dia. (mm)  4.000 r₁ = 81.9112 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 10.0742 (aspherical) d₂ = D2 (variable) r₃ =10.3535 (aspherical) d₃ = 4.3238 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−20.9984 (aspherical) d₄ = D4 (variable) r₅ = −10.0333 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3333 (aspherical) d₆ = D6(variable) r₇ = 11.3130 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−23.1581 (aspherical) d₈ = 0.5000 r₉ = 15.7417 (aspherical) d₉ = 22.5485n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.2615 r₁₁ = ∞ (fieldframe) d₁₁ = 2.5500 r₁₂ = 15.2310 (aspherical) d₁₂ = 15.5600 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −39.1300 d₁₃ = 1.7500 r₁₄ = 24.5529 d₁₄ =5.3200 n_(d14) = 1.49700 ν_(d14) = 81.54 r₁₅ = −15.8669 (aspherical) d₁₅= 17.0491 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2950 A₄ = 5.82582 × 10⁻⁶ A₆ = −2.91852 × 10⁻⁷ A₈ = 1.53866 × 10⁻⁹Third surface K = −0.2618 A₄ = −8.99427 × 10⁻⁵ A₆ = −3.14079 × 10⁻⁷ A₈ =−8.23133 × 10⁻⁹ Fourth surface K = −0.0224 A₄ = 8.74333 × 10⁻⁵ A₆ =−3.77249 × 10⁻⁷ A₈ = −3.31925 × 10⁻⁹ Fifth surface K = 0.2138 A₄ =6.11164 × 10⁻⁴ A₆ = −3.28266 × 10⁻⁵ A₈ = 7.55363 × 10⁻⁷ Sixth surface K= −0.0425 A₄ = 2.44411 × 10⁻⁵ A₆ = −2.80434 × 10⁻⁵ A₈ = 6.70880 × 10⁻⁷Eighth surface K = 0.1564 A₄ = 2.36396 × 10⁻⁴ A₆ = −1.54507 × 10⁻⁶ A₈ =3.28513 × 10⁻⁸ Ninth surface K = 0.0138 A₄ = 7.48388 × 10⁻⁶ A₆ =−1.90449 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Fifteenth surface K = 0.0000 A₄ = 5.20019 × 10⁻⁵ A₆ =1.50643 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2 9.1623 7.1846  3.4243 D4 4.9049 8.2975 16.2619 D6 6.61905.2041  1.0000 mh = 10.121 mm Conditions (1), (7) mh/fe = 0.674Condition (4) ν = 81.54 Conditions (2), (3) fe = 15.010 mm

[0405] Seventh Embodiment

[0406] In the real image mode finder optical system of this embodiment,as shown in FIGS. 30A-30D, the objective optical system includes, inorder from the object side, a first unit G1 with a negative refractingpower, a second unit G2 with a positive refracting power, a third unitG3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0407] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the prism P and the positivelens E1 and has a positive refracting power as a whole.

[0408] The image erecting means includes the prisms P1 and P2 and theprism P. In the real image mode finder optical system of the seventhembodiment, the intermediate image formed by the objective opticalsystem is interposed between the prism P2 and the prism P, and the fieldframe, such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

[0409] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by moving the second unit G2 and the thirdunit G3 along the optical axis.

[0410] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havefinite curvatures, that is, are configured as lens surfaces. Theentrance surface and the exit surface of the prism P also have finitecurvatures.

[0411] The prisms P1 and P2 and the prism P, as in the first embodimentshown in FIGS. 1-3, are provided with the reflecting surfaces along theoptical path so that the optical axis is bent to erect an image. Forexample, one reflecting surface provided in the prism P1 bends theoptical axis in the Y-Z plane; two reflecting surfaces provided in theprism P2 bend the optical axis in the Y-Z plane and the X-Z plane inthis order from the object side; and one reflecting surface provided inthe prism P bends the optical axis in the X-Z plane. In this way, anerect image is obtained. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangles of the optical axis bent by the reflecting surfaces of the prismP1 and the prism P are smaller than 90 degrees and the angles of theoptical axis bent by the two reflecting surfaces of the prism P2 arelarger than 90 degrees. The reflecting surfaces of the prism P1 and theprism P are coated with metal films, such as silver and aluminum. Thetwo reflecting surfaces of the prism P2 utilize total reflection.

[0412] However, the ways of bending the optical axis through the prismsand the angles of the optical axis bent by the reflecting surfaces arenot limited to the above description. For example, the angle of theoptical axis bent by the most field-frame-side reflecting surface of theprism P2 may be made smaller than 90 degrees so that this reflectingsurface is coated with a metal film. Moreover, the angle of the opticalaxis bent by the reflecting surface of the prism P may also be madelarger than 90 degrees so that this reflecting surface utilizes totalreflection.

[0413] The positive lens E1 is constructed so that diopter adjustmentcan be made in accordance with an observer's diopter.

[0414] Also, aberration characteristics in the seventh embodiment areshown in FIGS. 31A-31D, 32A-32D, 33A-33D, and 34A-34D.

[0415] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the seventhembodiment are shown below.

[0416] Numerical Data 7 Wide-angle position Middle position Telephotoposition m  0.743  1.015  2.070 ω (°) 23.875 17.526  8.746 f (mm) 11.14615.237 31.075 Pupil dia. (mm)  4.000 r₁ = 81.9602 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 10.0611 (aspherical) d₂ = D2 (variable) r₃ =10.3753 (aspherical) d₃ = 4.3253 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−20.8601 (aspherical) d₄ = D4 (variable) r₅ = −10.0315 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3315 (aspherical) d₆ = D6r₇ = 11.2984 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −23.0708(aspherical) d₈ = 0.5000 r₉ = 15.8095 (aspherical) d₉ = 22.5530 n_(d9) =1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.2570 r₁₁ = ∞ (field frame) d₁₁ =2.5500 r₁₂ = 15.4188 (aspherical) d₁₂ = 15.5600 n_(d12) = 1.52542ν_(d12) = 55.78 r₁₃ = −37.3902 d₁₃ = 1.7500 r₁₄ = 20.4078 d₁₄ = 5.3200n_(d14) = 1.43389 ν_(d14) = 95.15 r₁₅ = −14.4726 (aspherical) d₁₅ =17.0491 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2949 A₄ = 6.66017 × 10⁻⁶ A₆ = −2.62591 × 10⁻⁷ A₈ = 1.12121 × 10⁻⁹Third surface K = −0.2625 A₄ = −7.97190 × 10⁻⁵ A₆ = −6.29748 × 10⁻⁷ A₈ =−1.17464 × 10⁻⁹ Fourth surface K = −0.0226 A₄ = 9.61346 × 10⁻⁵ A₆ =−6.24988 × 10⁻⁷ A₈ = −2.63996 × 10⁻⁹ Fifth surface K = 0.2132 A₄ =6.22361 × 10⁻⁴ A₆ = −3.35122 × 10⁻⁵ A₈ = 7.43683 × 10⁻⁷ Sixth surface K= −0.0427 A₄ = 3.84712 × 10⁻⁵ A₆ = −2.91300 × 10⁻⁵ A₈ = 6.92795 × 10⁻⁷Eighth surface K = 0.1561 A₄ = 2.24263 × 10⁻⁴ A₆ = −1.03011 × 10⁻⁶ A₈ =3.32247 × 10⁻⁸ Ninth surface K = 0.0135 A₄ = −5.19982 × 10 ⁻⁶ A₆ =−1.46612 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Fifteenth surface K = 0.0000 A₄ = 7.35154 × 10⁻⁵ A₆ =2.26014 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2 9.1683 7.1925  3.4339 D4 4.8993 8.2891 16.2507 D6 6.61715.2031  1.0000 mh = 10.133 mm Conditions (1), (7) mh/fe = 0.675Condition (4) ν = 95.15 Conditions (2), (3) fe = 15.010 mm

[0417] Eighth Embodiment

[0418] In the real image mode finder optical system of this embodiment,as shown in FIGS. 35A-35D, the objective optical system includes, inorder from the object side, a first unit G1 with a negative refractingpower, a second unit G2 with a positive refracting power, a third unitG3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0419] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with a cemented lens component CEcomprised of a positive lens element CE1 and a negative lens element CE2and has a positive refracting power as a whole.

[0420] The image erecting means includes the prisms P1 and P2 and theprism P. In the real image mode finder optical system of the eighthembodiment, the intermediate image formed by the objective opticalsystem is interposed between the prism P2 and the prism P, and the fieldframe, such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

[0421] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by moving the second unit G2 and the thirdunit G3 along the optical axis.

[0422] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havefinite curvatures. The entrance surface and the exit surface of theprism P also have finite curvatures.

[0423] The prisms P1 and P2 and the prism P are provided with thereflecting surfaces along the optical path so that the optical axis isbent to erect an image. For example, the prism P1 is provided with onereflecting surface (for bending the optical axis in the Y-Z plane), theprism P2 is provided with two reflecting surfaces (for bending theoptical axis in the Y-Z plane and the X-Z plane), and the prism P isprovided with one reflecting surface (for bending the optical axis inthe X-Z plane) to erect the image. Also, the arrangement of thereflecting surfaces is based on that of a Porro prism. Angles made withthe optical axis bent by the reflecting surfaces are such that, forexample, the angles of the optical axis bent by the reflecting surfacesof the prism P1 and the prism P are smaller than 90 degrees and theangles of the optical axis bent by the two reflecting surfaces of theprism P2 are larger than 90 degrees. The reflecting surfaces of theprism P1 and the prism P are coated with metal films, such as silver andaluminum. The two reflecting surfaces of the prism P2 utilize totalreflection.

[0424] However, the ways of bending the optical axis through the prismsand the angles of the optical axis bent by the reflecting surfaces arenot limited to the above description. For example, the angle of theoptical axis bent by the most field-frame-side reflecting surface of theprism P2 may be made smaller than 90 degrees so that this reflectingsurface is coated with a metal film. Moreover, the angle of the opticalaxis bent by the reflecting surface of the prism P may also be madelarger than 90 degrees so that this reflecting surface utilizes totalreflection.

[0425] The cemented lens component CE is constructed so that diopteradjustment can be made in accordance with an observer's diopter.

[0426] In the eighth embodiment, the cemented lens component CEincluding, in order from the object side, the positive lens element andthe negative lens element is used to suppress the chromatic aberrationof magnification produced in the eyepiece optical system.

[0427] Also, aberration characteristics in the eighth embodiment areshown in FIGS. 36A-36D, 37A-37D, 38A-38D, and 39A-39D.

[0428] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the eighth embodimentare shown below.

[0429] Numerical Data 8 Wide-angle position Middle position Telephotoposition m  0.743  1.020  2.076 ω (°) 23.954 17.549  8.727 f (mm) 11.16015.304 31.158 Pupil dia. (mm)  4.000 r₁ = 75.9203 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 10.0850 (aspherical) d₂ = D2 (variable) r₃ =10.2485 (aspherical) d₃ = 4.2776 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−21.9093 d₄ = D4 (variable) r₅ = −10.0501 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3501 (aspherical) d₆ = D6(variable) r₇ = 11.5799 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−21.8697 (aspherical) d₈ = 0.5000 r₉ = 15.8360 (aspherical) d₉ = 22.6385n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.1715 r₁₁ = ∞ (fieldframe) d₁₁ = 2.5500 r₁₂ = 18.8734 (aspherical) d₁₂ = 15.5600 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −20.0934 d₁₃ = 1.7500 r₁₄ = 36.0448 d₁₄ =5.3393 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −13.2074 d₁₅ = 1.0000n_(d15) = 1.58423 ν_(d15) = 30.49 r₁₆ = −18.5585 (aspherical) d₁₆ =17.0491 r₁₇ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2950 A₄ = −2.88906 × 10⁻⁵ A₆ = 1.81910 × 10⁻⁷ A₈ = −1.52765 × 10⁻⁹Third surface K = −0.2463 A₄ = −1.12182 × 10⁻⁴ A₆ = −6.22353 × 10⁻⁷ A₈ =2.82153 × 10⁻⁹ Fourth surface K = −0.0226 A₄ = 8.40588 × 10⁻⁵ A₆ =−7.72274 × 10⁻⁷ A₈ = 6.21797 × 10⁻⁹ Fifth surface K = 0.2122 A₄ =1.04005 × 10⁻³ A₆ = −6.22976 × 10⁻⁵ A₈ = 1.48889 × 10⁻⁶ Sixth surface K= −0.0428 A₄ = 4.20510 × 10⁻⁴ A₆ = −5.35363 × 10⁻⁵ A₈ = 1.24406 × 10⁻⁶Eighth surface K = 0.1561 A₄ = 2.78620 × 10⁻⁴ A₆ = −1.75114 × 10⁻⁶ A₈ =1.84964 × 10⁻⁸ Ninth surface K = 0.0138 A₄ = 7.75842 × 10⁻⁵ A₆ =−2.54066 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Sixteenth surface K = 0.0000 A₄ = 1.54561 × 10⁻⁵ A₆ =6.06156 × 10⁻⁸ Wide-angle position Middle position Telephoto positionZoom data D2 9.1388 7.1293  3.3607 D4 4.9642 8.4021 16.3723 D6 6.63075.2010  0.9994 mh = 10.095 mm Conditions (1), (7) mh/fe = 0.673Conditions (2), (3) fe = 15.010 mm Conditions (5), (6) vp − vn = 25.29

[0430] Ninth Embodiment

[0431] In the real image mode finder optical system of this embodiment,as shown in FIGS. 40A-40D, the objective optical system includes, inorder from the object side, a first unit G1 with a negative refractingpower, a second unit G2 with a positive refracting power, a third unitG3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0432] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the cemented lens componentCE comprised of the positive lens element CE1 and the negative lenselement CE2 and has a positive refracting power as a whole.

[0433] The image erecting means includes the prisms P1 and P2 and theprism P. In the real image mode finder optical system of the ninthembodiment, the intermediate image formed by the objective opticalsystem is interposed between the prism P2 and the prism P, and the fieldframe, such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

[0434] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by moving the second unit G2 and the thirdunit G3 along the optical axis.

[0435] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havefinite curvatures. The entrance surface and the exit surface of theprism P also have finite curvatures.

[0436] The prisms P1 and P2 and the prism P are provided with thereflecting surfaces along the optical path so that the optical axis isbent to erect an image. For example, the prism P1 is provided with onereflecting surface (for bending the optical axis in the Y-Z plane), theprism P2 is provided with two reflecting surfaces (for bending theoptical axis in the Y-Z plane and the X-Z plane), and the prism P isprovided with one reflecting surface (for bending the optical axis inthe X-Z plane) to erect the image. Also, the arrangement of thereflecting surfaces is based on that of a Porro prism. Angles made withthe optical axis bent by the reflecting surfaces are such that, forexample, the angles of the optical axis bent by the reflecting surfacesof the prism P1 and the prism P are smaller than 90 degrees and theangles of the optical axis bent by the two reflecting surfaces of theprism P2 are larger than 90 degrees. The reflecting surfaces of theprism P1 and the prism P are coated with metal films, such as silver andaluminum. The two reflecting surfaces of the prism P2 utilize totalreflection.

[0437] However, the ways of bending the optical axis through the prismsand the angles of the optical axis bent by the reflecting surfaces arenot limited to the above description. For example, the angle of theoptical axis bent by the most field-frame-side reflecting surface of theprism P2 may be made smaller than 90 degrees so that this reflectingsurface is coated with a metal film. Moreover, the angle of the opticalaxis bent by the reflecting surface of the prism P may also be madelarger than 90 degrees so that this reflecting surface utilizes totalreflection.

[0438] The cemented lens component CE is constructed so that diopteradjustment can be made in accordance with an observer's diopter.

[0439] In the ninth embodiment, the cemented lens component CEincluding, in order from the object side, the positive lens element andthe negative lens element is used to suppress the chromatic aberrationof magnification produced in the eyepiece optical system.

[0440] Also, aberration characteristics in the ninth embodiment areshown in FIGS. 41A-41D, 42A-42D, 43A-43D, and 44A-44D.

[0441] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the ninth embodimentare shown below.

[0442] Numerical Data 9 Wide-angle position Middle position Telephotoposition m  0.745  1.019  2.078 ω (°) 23.864 17.523  8.748 f (mm) 11.17915.288 31.185 Pupil dia. (mm)  4.000 r₁ = 83.1968 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 10.0574 (aspherical) d₂ = D2 (variable) r₃ =10.4051 (aspherical) d₃ = 4.3247 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−20.6708 (aspherical) d₄ = D4 (variable) r₅ = −10.0283 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3283 (aspherical) d₆ = D6(variable) r₇ = 11.0837 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−23.2992 (aspherical) d₈ = 0.5000 r₉ = 16.1348 (aspherical) d₉ = 22.5851n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.2249 r₁₁ = ∞ (fieldframe) d₁₁ = 2.5500 r₁₂ = 15.1194 (aspherical) d₁₂ = 15.5600 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −32.9857 d₁₃ = 1.7500 r₁₄ = 22.3114 d₁₄ =1.0000 n_(d14) = 1.58423 ν_(d14) = 30.49 r₁₅ = 13.0456 d₁₅ = 5.4129n_(d15) = 1.52542 ν_(d15) = 55.78 r₁₆ = −18.6581 (aspherical) d₁₆ =17.0491 r₁₇ = ∞ (eyepiece) Aspherical coefficients Second surface K =−1.2945 A₄ = 9.89743 × 10⁻⁶ A₆ = −4.30715 × 10⁻⁷ A₈ = 2.58833 × 10⁻⁹Third surface K = −0.2627 A₄ = −6.69210 × 10⁻⁵ A₆ = −9.19006 × 10⁻⁷ A₈ =6.64337 × 10⁻¹⁰ Fourth surface K = −0.0228 A₄ = 1.06273 × 10⁻⁴ A₆ =−8.28362 × 10⁻⁷ A₈ = 3.85729 × 10⁻⁹ Fifth surface K = 0.2133 A₄ =6.06366 × 10⁻⁴ A₆ = −2.97302 × 10⁻⁵ A₈ = 5.98935 × 10⁻⁷ Sixth surface K= −0.0427 A₄ = 4.82034 × 10⁻⁵ A₆ = −2.89969 × 10⁻⁵ A₈ = 6.72146 × 10⁻⁷Eighth surface K = 0.1560 A₄ = 2.50445 × 10⁻⁴ A₆ = −1.47471 × 10⁻⁶ A₈ =4.11057 × 10⁻⁸ Ninth surface K = 0.0136 A₄ = 5.39717 × 10⁻⁶ A6 =−1.68771 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Sixteenth surface K = 0.0000 A₄ = 3.44659 × 10⁻⁵ A₆ =1.08095 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2 9.1868 7.2088  3.4518 D4 4.8856 8.2783 16.2383 D6 6.61295.1982  0.9952 mh = 10.217 mm Conditions (1), (7) mh/fe = 0.681Conditions (2), (3) fe = 15.006 mm Conditions (5), (6) vp − vn = 25.29

[0443] Tenth Embodiment

[0444] In the real image mode finder optical system of this embodiment,as shown in FIGS. 45A-45D, the objective optical system includes, inorder from the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0445] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the negative lens L1 and thepositive lens E1 and has a positive refracting power as a whole.

[0446] The image erecting means includes the prisms P1 and P2. In thereal image mode finder optical system of the tenth embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P2 and the negative lens L1, and the field frame, suchas that shown in FIG. 4, is placed in the proximity of its imagingposition.

[0447] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

[0448] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of each of the prisms P1 and P2 have finite curvatures.

[0449] The prisms P1 and P2 are provided with reflecting surfaces alongthe optical path so that the optical axis is bent to obtain an erectimage. For example, the prism P1 is provided with one reflecting surface(for bending the optical axis in the Y-Z plane) and the prism P2 isprovided with three reflecting surfaces (for bending the optical axisonce in the Y-Z plane and twice in the X-Z plane in this order from theobject side) to erect the image. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangle of the optical axis bent by the reflecting surface of the prism P1is smaller than 90 degrees, while the angles of the optical axis bent bytwo reflecting surfaces of the prism P2 are larger than 90 degrees andthe angle of the optical axis bent by the remaining one reflectingsurface is smaller than 90 degrees. The reflecting surfaces makingangles smaller than 90 degrees are coated with metal films, such assilver and aluminum. The reflecting surfaces of angles larger than 90degrees utilize total reflection. The positive lens E1 is constructed sothat diopter adjustment can be made in accordance with an observer'sdiopter.

[0450] In the tenth embodiment, low-dispersion glass is used for thepositive lens E1 to suppress chromatic aberration of magnificationproduced in the eyepiece optical system.

[0451] Also, aberration characteristics in the tenth embodiment areshown in FIGS. 46A-46D, 47A-47D, 48A-48D, and 49A-49D.

[0452] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the tenth embodimentare shown below.

[0453] Numerical Data 10 Wide-angle position Middle position Telephotoposition m  0.686  1.177  2.019 ω (°) 26.700 15.294  8.889 f (mm) 10.29017.650 30.261 Pupil dia. (mm)  4.000 r₁ = −35.4073 d₁ = 1.3547 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 15.7324 (aspherical) d₂ = D2 (variable) r₃ =14.1173 (aspherical) d₃ = 4.2036 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ =−19.7136 d₄ = D4 (variable) r₅ = −21.3268 d₅ = 1.0000 n_(d5) = 1.58423ν_(d5) = 30.49 r₆ = 15.4585 (aspherical) d₆ = D6 (variable) r₇ = 47.9547d₇ = 14.7087 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −16.9222 (aspherical)d₈ = 0.5000 r₉ = 40.5011 d₉ = 39.7256 n_(d9) = 1.52542 ν_(d9) = 55.78r₁₀ = −22.4670 d₁₀ = 4.0295 r₁₁ = ∞ (field frame) d₁₁ = 7.6484 r₁₂ =−6.8411 (aspherical) d₁₂ = 3.0616 n_(d12) = 1.58423 ν_(d12) = 30.49 r₁₃= −9.5101 d₁₃ = 1.9354 r₁₄ = 16.4813 d₁₄ = 5.2395 n_(d14) = 1.49700ν_(d14) = 81.54 r₁₅ = −12.4181 (aspherical) d₁₅ = 15.7651 r₁₆ = ∞(eyepoint) Aspherical coefficients Second surface K = −1.3019 A₄ =−1.03082 × 10⁻⁴ A₆ = 1.18309 × 10⁻⁶ A₈ = −3.69689 × 10⁻⁹ Third surface K= −0.1784 A₄ = −1.31901 × 10⁻⁴ A₆ = 1.62576 × 10⁻⁷ A₈ = −5.25998 × 10⁻¹⁰Sixth surface K = −0.0760 A₄ = −7.29856 × 10⁻⁵ A₆ = −1.57784 × 10⁻⁶ A₈ =2.85950 × 10⁻⁸ Eighth surface K = 0.1940 A₄ = 3.47928 × 10⁻⁵ A₆ =5.46298 × 10⁻⁸ A₈ = 1.40140 × 10⁻⁹ Twelfth surface K = 0.0000 A₄ =−2.29965 × 10⁻⁴ A₆ = −5.49255 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ =1.23613 × 10⁻⁴ A₆ = 7.32239 × 10⁻⁷ Wide-angle position Middle positionTelephoto position Zoom data D2 25.8585 12.8666  7.9000 D4  1.0000 9.3310 20.3050 D6  3.2733  5.0026  1.7063 mh = 9.539 mm Conditions (1),(7) mh/fe = 0.636 Condition (4) ν = 81.54 Conditions (2), (3) fe =14.990 mm

[0454] Eleventh Embodiment

[0455] In the real image mode finder optical system of this embodiment,as shown in FIGS. 50A-50D, the objective optical system includes, inorder from the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0456] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the negative lens L1 and thecemented lens component CE comprised of the negative lens element CE 2and the positive lens element CE1, and has a positive refracting poweras a whole.

[0457] The image erecting means includes the prisms P1 and P2. In thereal image mode finder optical system of the eleventh embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P2 and the negative lens L1, and the field frame, suchas that shown in FIG. 4, is placed in the proximity of its imagingposition.

[0458] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

[0459] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of each of the prisms P1 and P2 have finite curvatures.

[0460] The prisms P1 and P2 are provided with reflecting surfaces alongthe optical path so that the optical axis is bent to obtain an erectimage. For example, the prism P1 is provided with one reflecting surface(for bending the optical axis in the Y-Z plane) and the prism P2 isprovided with three reflecting surfaces (for bending the optical axisonce in the Y-Z plane and twice in the X-Z plane in this order from theobject side) to erect the image. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangle of the optical axis bent by the reflecting surface of the prism P1is smaller than 90 degrees, while the angles of the optical axis bent bytwo reflecting surfaces of the prism P2 are larger than 90 degrees andthe angle of the optical axis bent by the remaining one reflectingsurface is smaller than 90 degrees. The reflecting surfaces makingangles smaller than 90 degrees are coated with metal films, such assilver and aluminum. The reflecting surfaces of angles larger than 90degrees utilize total reflection. The cemented lens component CE isconstructed so that diopter adjustment can be made in accordance with anobserver's diopter.

[0461] In the eleventh embodiment, the cemented lens component CEincluding, in order from the object side, the negative lens element andthe positive lens element is used to suppress the chromatic aberrationof magnification produced in the eyepiece optical system.

[0462] Also, aberration characteristics in the eleventh embodiment areshown in FIGS. 51A-51D, 52A-52D, 53A-53D, and 54-54D.

[0463] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the eleventhembodiment are shown below.

[0464] Numerical Data 11 Wide-angle position Middle position Telephotoposition m  0.685  1.175  2.016 ω (°) 26.509 15.216  8.803 f (mm) 10.28917.629 30.259 Pupil dia. (mm)  4.000 r₁ = −31.2936 d₁ = 1.3442 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 16.8814 (aspherical) d₂ = D2 (variable) r₃ =14.1167 (aspherical) d₃ = 4.5120 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ =−20.4840 d₄ = D4 (variable) r₅ = −20.2406 d₅ = 0.9963 n_(d5) = 1.58423ν_(d5) = 30.49 r₆ = 14.9676 (aspherical) d₆ = D6 (variable) r₇ = 41.4899d₇ = 14.6927 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −17.9428 (aspherical)d₈ = 0.5000 r₉ = 34.5533 d₉ = 39.7402 n_(d9) = 1.52542 ν_(d9) = 55.78r₁₀ = −28.4392 d₁₀ = 4.5510 r₁₁ = ∞ (field frame) d₁₁ = 7.9719 r₁₂ =−9.6322 (aspherical) d₁₂ = 3.1829 n_(d12) = 1.58423 ν_(d12) = 30.49 r₁₃= −10.6815 d₁₃ = 1.6105 r₁₄ = 19.4893 d₁₄ = 1.0000 n_(d14) = 1.58423ν_(d14) = 30.49 r₁₅ = 13.6490 d₁₅ = 5.4672 n_(d15) = 1.49241 ν_(d15) =57.66 r₁₆ = −12.4053 (aspherical) d₁₆ = 15.7651 r₁₇ = ∞ (eyepoint)Aspherical coefficients Second surface K = −1.3018 A₄ = −1.08269 × 10⁻⁴A₆ = 9.30175 × 10⁻⁷ A₈ = −1.42679 × 10⁻⁹ Third surface K = −0.1791 A₄ =−1.31719 × 10⁻⁴ A₆ = 1.67274 × 10⁻⁷ A₈ = −6.28754 × 10⁻¹⁰ Sixth surfaceK = −0.0761 A₄ = −1.10385 × 10⁻⁴ A₆ = −3.75495 × 10⁻⁷ A₈ = 2.90075 ×10⁻⁹ Eighth surface K = 0.1945 A₄ = 3.40022 × 10⁻⁵ A₆ = −8.32444 × 10⁻⁸A₈ = 2.90545 × 10⁻⁹ Twelfth surface K = 0.0000 A₄ = −2.80853 × 10⁻⁴ A₆ =−6.97108 × 10⁻⁶ Sixteenth surface K = 0.0000 A₄ = 3.07353 × 10⁻⁵ A₆ =9.18614 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2 25.8073 13.2103  8.2556 D4  0.9957  9.3832 20.5408 D6 3.5101  4.5817  1.6440 mh = 9.486 mm Conditions (1), (7) mh/fe = 0.632Conditions (2), (3) fe = 15.010 mm Conditions (5), (6) vp − vn = 27.17

[0465] Twelfth Embodiment

[0466] The real image mode finder optical system of this embodiment, asshown in FIGS. 55A-55C, has nearly the same arrangement as that of thefirst embodiment with the exception of lens data.

[0467] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the twelfthembodiment are shown below.

[0468] Numerical Data 12 Wide-angle position Middle position Telephotoposition m  0.530  1.007  2.050 ω (°) 33.694 17.618  8.796 f (mm)  8.48216.100 32.782 Pupil dia. (mm)  4.000 r₁ = 52.6894 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 9.9227 (aspherical) d₂ = D2 (variable) r₃ =10.2741 (aspherical) d₃ = 4.2589 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−23.8681 (aspherical) d₄ = D4 (variable) r₅ = −10.3480 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.6480 (aspherical) d₆ = D6(variable) r₇ = 11.1372 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−26.1339 (aspherical) d₈ = 0.5000 r₉ = 15.5869 (aspherical) d₉ = 22.3572n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.4528 r₁₁ = ∞ (fieldframe) d₁₁ = 3.0665 r₁₂ = 15.8132 (aspherical) d₁₂ = 15.9408 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −75.7570 d₁₃ = 2.0915 r₁₄ = 27.2996 d₁₄ =4.8098 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −16.0615 (aspherical) d₁₅= 16.8220 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2951 A₄ = 2.66909 × 10⁻⁵ A₆ = −2.25605 × 10⁻⁷ A₈ = 9.99104 × 10⁻¹¹Third surface K = −0.2614 A₄ = −8.86459 × 10⁻⁵ A₆ = −2.02523 × 10⁻⁷ A₈ =−5.25729 × 10⁻⁹ Fourth surface K = −0.0224 A₄ = 6.51575 × 10⁻⁵ A₆ =−1.53327 × 10⁻⁷ A₈ = −1.18392 × 10⁻⁹ Fifth surface K = 0.2138 A₄ =4.33241 × 10⁻⁴ A₆ = −1.93785 × 10⁻⁵ A₈ = 4.02985 × 10⁻⁷ Sixth surface K= −0.0427 A₄ = −9.91769 × 10⁻⁵ A₆ = −1.51811 × 10⁻⁵ A₈ = 3.40669 × 10⁻⁷Eighth surface K = 0.1565 A₄ = 2.28575 × 10⁻⁴ A₆ = −1.22359 × 10⁻⁷ A₈ =3.27751 × 10⁻⁸ Ninth surface K = 0.0140 A₄ = 4.56644 × 10⁻⁶ A₆ =−9.81069 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ = −7.24335 × 10⁻⁴ A₆ =3.64409 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ = 4.99493 × 10⁻⁵ A₆ =9.74998 × 10⁻⁸ Wide-angle position Middle position Telephoto positionZoom data D2   11.4582    6.8773    3.0038 D4    1.2808    8.5674  16.7674 D6    8.0121    5.3064    0.9799 mh = 10.692 mm f123 −11.144−21.243 −44.469 m23    0.529    1.000    2.038 m2  −1.000 m3  −1.000Condition (9) MG45 −0.763  −0.765  −0.767 Conditions (1), (7) mh/fe =0.669 Conditions (2), (3) fe = 15.991 mm Condition (8) Φ(mh/2) =−0.406970 (1/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.389Condition (12) f2/f3 = −1.618 Condition (13) fw/fFw = −0.761 Condition(14) fT/fFT = −0.737 Condition (15) mT/mW = 3.865 Condition (16)fw/fw123 = −0.761 Condition (17) fT/fT123 = −0.737

[0469] Thirteenth Embodiment

[0470] The real image mode finder optical system of this embodiment, asshown in FIGS. 56A-56C, has nearly the same arrangement as that of thefirst embodiment with the exception of lens data.

[0471] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the thirteenthembodiment are shown below.

[0472] Numerical Data 13 Wide-angle position Middle position Telephotoposition m  0.533  1.007  2.050 ω (°) 33.897 17.661  8.803 f (mm)  7.46814.111 28.722 Pupil dia. (mm)  4.000 r₁ = 166.7316 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 10.3218 (aspherical) d₂ = D2 (variable) r₃ =10.2841 (aspherical) d₃ = 4.3636 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−19.9166 (aspherical) d₄ = D4 (variable) r₅ = −9.8214 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.1214 (aspherical) d₆ = D6(variable) r₇ = 13.2873 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−17.5762 (aspherical) d₈ = 0.5000 r₉ = 15.4406 (aspherical) d₉ = 22.6932n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.1168 r₁₁ = ∞ (fieldframe) d₁₁ = 2.4325 r₁₂ = 28.5591 (aspherical) d₁₂ = 14.7924 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −24.5754 d₁₃ = 1.2620 r₁₄ = 27.5003 d₁₄ =4.1395 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −16.2956 (aspherical) d₁₅= 16.6524 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2951 A₄ = −9.85470 × 10⁻⁶ A₆ = −3.31289 × 10⁻⁷ A₈ = 3.00060 × 10⁻⁹Third surface K = −0.2607 A₄ = −9.27092 × 10⁻⁵ A₆ = −8.01222 × 10⁻⁷ A₈ =2.80942 × 10⁻⁹ Fourth surface K = −0.0224 A₄ = 1.02300 × 10⁻⁴ A₆ =−7.73167 × 10⁻⁷ A₈ = 5.82839 × 10⁻⁹ Fifth surface K = 0.2137 A₄ =5.86855 × 10⁻⁴ A₆ = −2.95943 × 10⁻⁵ A₈ = 6.45936 × 10⁻⁷ Sixth surface K= −0.0425 A₄ = −2.30372 × 10⁻⁵ A₆ = −2.55725 × 10⁻⁵ A₈ = 6.22366 × 10⁻⁷Eighth surface K = 0.1564 A₄ = 1.56106 × 10⁻⁴ A₆ = −7.63871 × 10⁻⁸ A₈ =4.09536 × 10⁻⁹ Ninth surface K = 0.0137 A₄ = 9.52536 × 10⁻⁷ A₆ =−1.05084 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.23450 × 10⁻³ A₆ =1.00000 × 10⁻⁵ Fifteenth surface K = 0.0000 A₄ = 3.90391 × 10⁻⁵ A₆ =1.54761 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2   11.7540    7.4253    3.7541 D4    1.2500    8.1247  15.8923 D6    7.6424    5.0964    1.0000 mh = 9.279 mm f123 −10.011−18.982 −39.511 m23    0.531    1.000    2.036 m2  −1.000 m3  −1.000Condition (9) MG45 −0.748  −0.749  −0.751 Conditions (1), (7) mh/fe =0.662 Conditions (2), (3) fe = 14.010 mm Condition (8) Φ(mh/2) =−0.395473 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.319Condition (12) f2/f3 = −1.622 Condition (13) fw/fFw = −0.746 Condition(14) fT/fFT = −0.727 Condition (15) mT/mW = 3.846 Condition (16)fw/fw123 = −0.746 Condition (17) fT/fT123 = −0.727

[0473] Fourteenth Embodiment

[0474] The real image mode finder optical system of this embodiment, asshown in FIGS. 57A-57C, has nearly the same arrangement as that of thefirst embodiment with the exception of lens data.

[0475] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the fourteenthembodiment are shown below.

[0476] Numerical Data 14 Wide-angle position Middle position Telephotoposition m  0.530  1.011  2.054 ω (°) 33.791 17.591  8.810 f (mm)  7.96215.170 30.830 Pupil dia. (mm)  4.000 r₁ = 82.9717 d₁ = 1.0000 n_(d1) =1.58425 ν_(d1) = 30.35 r₂ = 10.0913 (aspherical) d₂ = D2 (variable) r₃ =10.3969 (aspherical) d₃ = 4.2911 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−21.6082 (aspherical) d₄ = D4 (variable) r₅ = −11.4300 d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 9.3984 (aspherical) d₆ = D6(variable) r₇ = 11.1076 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−24.3057 (aspherical) d₈ = 0.5000 r₉ = 15.7603 (aspherical) d₉ = 22.4265n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.2691 r₁₁ = ∞ (fieldframe) d₁₁ = 2.5500 r₁₂ = 15.9134 (aspherical) d₁₂ = 15.5881 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −39.1000 d₁₃ = 1.7582 r₁₄ = 25.7997(aspherical) d₁₄ = 5.1865 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ =−16.7689 (aspherical) d₁₅ = 16.8782 r₁₆ = ∞ (eyepoint) Asphericalcoefficients Second surface K = −1.2943 A₄ = −9.84819 × 10⁻⁶ A₆ =−2.39182 × 10⁻⁸ A₈ = 4.94427 × 10⁻¹⁰ Third surface K = −0.2438 A₄ =−1.13792 × 10⁻⁴ A₆ = −6.83279 × 10⁻⁸ A₈ = −6.63089 × 10⁻⁹ Fourth surfaceK = −0.0218 A₄ = 6.76356 × 10⁻⁵ A₆ = −1.19790 × 10⁻⁷ A₈ = −2.64472 ×10⁻⁹ Sixth surface K = −0.0422 A₄ = −5.28848 × 10⁻⁴ A₆ = 2.13243 × 10⁻⁶A₈ = 1.98353 × 10⁻⁸ Eighth surface K = 0.1608 A₄ = 1.86541 × 10⁻⁴ A₆ =1.81579 × 10⁻⁷ A₈ = 3.74182 × 10⁻⁸ Ninth surface K = 0.0115 A₄ =−3.79724 × 10⁻⁵ A₆ = −6.23075 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ =−1.19998 × 10⁻³ A₆ = 1.07234 × 10⁻⁵ Fourteenth surface K = 0.0000 A₄ =1.76029 × 10⁻⁵ A₆ = 3.42514 × 10⁻⁷ Fifteenth surface K = 0.0000 A₄ =6.14363 × 10⁻⁵ A₆ = 4.37825 × 10⁻⁷ Wide-angle position Middle positionTelephoto position Zoom data D2   12.0419    7.5075    3.7196 D4   1.1332    8.3326   16.3538 D6    7.8982    5.2332    1.0000 mh =10.098 mm f123 −10.392 −19.874 −41.387 m23    0.526    1.000    2.034 m2 −1.000 m3  −1.000 Condition (9) MG45 −0.768   −0.770   −0.772Conditions (1), (7) mh/fe = 0.673 Conditions (2), (3) fe = 15.010 mmCondition (8) Φ(mh/2) = −0.377550 (l/mm) Condition (10) β3 = −1.000Condition (11) SF2 = −0.350 Condition (12) f2/f3 = −1.615 Condition (13)fw/fFw = −0.766 Condition (14) fT/fFT = −0.745 Condition (15) mT/mW =3.872 Condition (16) fw/fw123 = −0.766 Condition (17) fT/fT123 = −0.745

[0477] Fifteenth Embodiment

[0478] The real image mode finder optical system of this embodiment, asshown in FIGS. 58A-58C, has nearly the same arrangement as that of thefirst embodiment with the exception of lens data.

[0479] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the fifteenthembodiment are shown below.

[0480] Numerical Data 15 Wide-angle position Middle position Telephotoposition m  0.429  0.813  1.663 ω (°) 33.665 17.724  8.889 f (mm)  7.38413.997 28.641 Pupil dia. (mm)  4.000 r₁ = 107.4567 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 10.2589 (aspherical) d₂ = D2 (variable) r₃ =10.2029 (aspherical) d₃ = 4.4631 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−20.4728 (aspherical) d₄ = D4 (variable) r₅ = −9.3096 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3604 (aspherical) d₆ = D6(variable) r₇ = 16.9815 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−13.8071 (aspherical) d₈ = 0.5000 r₉ = 15.6162 (aspherical) d₉ = 22.4902n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.3198 r₁₁ = ∞ (fieldframe) d₁₁ = 3.8080 r₁₂ = 24.6624 (aspherical) d₁₂ = 15.9445 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −144.7239 d₁₃ = 2.0644 r₁₄ = 37.1434 d₁₄ =4.1276 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −14.1033 (aspherical) d₁₅= 16.7947 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2993 A₄ = 5.71536 × 10⁻⁵ A₆ = −1.74731 × 10⁻⁶ A₈ = 9.48321 × 10⁻⁹Third surface K = −0.2562 A₄ = −1.82646 × 10⁻⁵ A₆ = −1.79005 × 10⁻⁶ A₈ =5.13165 × 10⁻⁹ Fourth surface K = −0.0200 A₄ = 1.47200 × 10⁻⁴ A₆ =−1.56976 × 10⁻⁶ A₈ = 1.27897 × 10⁻⁸ Fifth surface K = 0.2127 A₄ =5.41270 × 10⁻⁴ A₆ = −3.32639 × 10⁻⁵ A₈ = 5.81147 × 10⁻⁷ Sixth surface K= −0.0433 A₄ = −1.09499 × 10⁻⁴ A₆ = −2.68424 × 10⁻⁵ A₈ = 6.74415 × 10⁻⁷Eighth surface K = 0.1546 A₄ = 2.00697 × 10⁻⁴ A₆ = −1.61566 × 10⁻⁶ A₈ =−3.13569 × 10⁻⁹ Ninth surface K = 0.0164 A₄ = 6.95918 × 10⁻⁵ A₆ =−2.13186 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −4.54314 × 10⁻⁴ A₆ =−3.43968 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ = 4.97954 × 10⁻⁵ A₆ =1.10003 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2   11.2714    6.9682    3.2721 D4    1.6105    8.4616  16.2351 D6    7.6649    5.1170    1.0397 mh = 9.349 mm f123 −10.318−19.605 −41.020 m23    0.530    1.000    2.042 m2  −1.000 m3  −1.000Condition (9) MG45 −0.717  −0.720  −0.722 Conditions (1), (7) mh/fe =0.543 Conditions (2), (3) fe = 17.226 mm Condition (8) Φ(mh/2) =−0.390191 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.335Condition (12) f2/f3 = −1.656 Condition (13) fw/fFw = −0.716 Condition(14) fT/fFT = −0.698 Condition (15) mT/mW = 3.879 Condition (16)fw/fw123 = −0.716 Condition (17) fT/fT123 = −0.698

[0481] Sixteenth Embodiment

[0482] The real image mode finder optical system of this embodiment, asshown in FIGS. 59A-59C, has nearly the same arrangement as that of thefirst embodiment with the exception of lens data.

[0483] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the sixteenthembodiment are shown below.

[0484] Numerical Data 16 Wide-angle position Middle position Telephotoposition m  0.429  0.809  2.024 ω (°) 33.860 17.674  7.199 f (mm)  7.43914.047 35.124 Pupil dia. (mm)  4.000 r₁ = 244.6491 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 10.7182 (aspherical) d₂ = D2 (variable) r₃ =9.8239 (aspherical) d₃ = 4.5281 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−19.6580 (aspherical) d₄ = D4 (variable) r₅ = −9.4259 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 9.7259 (aspherical) d₆ = D6(variable) r₇ = 13.6837 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−17.5090 (aspherical) d₈ = 0.5000 r₉ = 15.6690 (aspherical) d₉ = 22.4657n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.3443 r₁₁ = ∞ (fieldframe) d₁₁ = 4.2463 r₁₂ = 24.2774 (aspherical) d₁₂ = 15.9476 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −225.2944 d₁₃ = 2.0463 r₁₄ = 37.1333 d₁₄ =3.6458 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −14.1787 (aspherical) d₁₅= 16.8295 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.3022 A₄ = 1.94109 × 10⁻⁵ A₆ = −1.53742 × 10⁻⁶ A₈ = 9.18621 × 10⁻⁹Third surface K = −0.2549 A₄ = −7.62311 × 10⁻⁵ A₆ = −2.11044 × 10⁻⁶ A₈ =9.22506 × 10⁻⁹ Fourth surface K = −0.0175 A₄ = 1.18065 × 10⁻⁴ A₆ =−1.28525 × 10⁻⁶ A₈ = 1.15858 × 10⁻⁸ Fifth surface K = 0.2594 A₄ =7.73262 × 10⁻⁴ A₆ = −4.07569 × 10⁻⁵ A₈ = 6.35774 × 10⁻⁷ Sixth surface K= −0.0434 A₄ = 2.49683 × 10⁻⁵ A₆ = −3.63701 × 10⁻⁵ A₈ = 8.31505 × 10⁻⁷Eighth surface K = 0.1534 A₄ = 1.67581 × 10⁻⁴ A₆ = −1.34210 × 10⁻⁶ A₈ =5.76435 × 10⁻⁹ Ninth surface K = 0.0177 A₄ = 9.17386 × 10⁻⁶ A₆ =−1.80151 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −3.02442 × 10⁻⁴ A₆ =−2.91068 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ = 5.38216 × 10⁻⁵ A₆ =6.59977 × 10⁻⁸ Wide-angle position Middle position Telephoto positionZoom data D2   10.3532    6.2169    1.8288 D4    1.2500    7.8558  17.6530 D6    8.8787    6.4091    1.0000 mh = 9.259 mm f123 −10.214−19.332 −50.207 m23    0.532    1.000    2.500 m2  −1.000 m3  −1.000Condition (9) MG45 −0.730  −0.732  −0.735 Conditions (1), (7) mh/fe =0.534 Conditions (2), (3) fe = 17.354 mm Condition (8) Φ(mh/2) =−0.263294 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.334Condition (12) f2/f3 = −1.638 Condition (13) fw/fFw = −0.728 Condition(14) fT/fFT = −0.700 Condition (15) mT/mW = 4.722 Condition (16)fw/fw123 = −0.728 Condition (17) fT/fT123 = −0.700

[0485] Seventeenth Embodiment

[0486] The real image mode finder optical system of this embodiment, asshown in FIGS. 60A-60C, has nearly the same arrangement as that of thefirst embodiment with the exception of lens data.

[0487] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the seventeenthembodiment are shown below.

[0488] Numerical Data 17 Wide-angle position Middle position Telephotoposition m  0.427  0.806  2.149 ω (°) 34.100 17.683  6.723 f (mm)  7.35813.901 37.053 Pupil dia. (mm)  4.000 r₁ = −713.7698 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 11.0797 (aspherical) d₂ = D2 (variable) r₃ =9.7135 (aspherical) d₃ = 4.6200 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−18.4096 (aspherical) d₄ = D4 (variable) r₅ = −9.1335 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 9.4327 (aspherical) d₆ = D6(variable) r₇ = 13.0353 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−18.2574 (aspherical) d₈ = 0.5000 r₉ = 15.8017 (aspherical) d₉ = 22.4291n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.3809 r₁₁ = ∞ (fieldframe) d₁₁ = 4.1914 r₁₂ = 23.7178 (aspherical) d₁₂ = 15.9419 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −188.7242 d₁₃ = 2.0225 r₁₄ = 38.0414 d₁₄ =3.6351 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −14.0922 (aspherical) d₁₅= 16.8589 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.3025 A₄ = −3.21798 × 10⁻⁵ A₆ = −7.78889 × 10⁻⁷ A₈ = 5.08606 × 10⁻⁹Third surface K = −0.2547 A₄ = −1.33313 × 10⁻⁴ A₆ = −1.48099 × 10⁻⁶ A₈ =7.55992 × 10⁻⁹ Fourth surface K = −0.0172 A₄ = 1.11743 × 10⁻⁴ A₆ =−9.24392 × 10⁻⁷ A₈ = 9.33552 × 10⁻⁹ Fifth surface K = 0.2714 A₄ =1.27697 × 10⁻³ A₆ = −8.18736 × 10⁻⁵ A₈ = 1.94631 × 10⁻⁶ Sixth surface K= −0.0432 A₄ = 3.65213 × 10⁻⁴ A₆ = −6.62961 × 10⁻⁵ A₈ = 1.63076 × 10⁻⁶Eighth surface K = 0.1534 A₄ = 1.31305 × 10⁻⁴ A₆ = −7.77237 × 10⁻⁷ A₈ =1.72405 × 10⁻⁸ Ninth surface K = 0.0176 A₄ = −4.34110 × 10⁻⁵ A₆ =−9.40302 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ = −2.47396 × 10⁻⁴ A₆ =−3.97394 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ = 5.72418 × 10⁻⁵ A₆ =3.57168 × 10⁻⁸ Wide-angle position Middle position Telephoto positionZoom data D2   10.0156    5.9870    1.4776 D4    1.2500    7.6739  17.9124 D6    9.1244    6.7292    1.0000 mh = 9.156 mm f123  −9.916−18.774 −52.236 m23    0.532    1.000    2.667 m2  −1.000 m3  −1.000Condition (9) MG45 −0.744  −0.746  −0.748 Conditions (1), (7) mh/fe =0.531 Conditions (2), (3) fe = 17.239 mm Condition (8) Φ(mh/2) =−0.251090 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.309Condition (12) f2/f3 = −1.647 Condition (13) fw/fFw = −0.742 Condition(14) fT/fFT = −0.709 Condition (15) mT/mW = 5.035 Condition (16)fw/fw123 = −0.742 Condition (17) fT/fT123 = −0.709

[0489] Eighteenth Embodiment

[0490] The real image mode finder optical system of this embodiment, asshown in FIGS. 61A-61C, has nearly the same arrangement as that of thefirst embodiment with the exception of lens data.

[0491] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the eighteenthembodiment are shown below.

[0492] Numerical Data 18 Wide-angle position Middle position Telephotoposition m  0.435  0.824  1.691 ω (°) 33.426 17.596  8.847 f (mm)  7.65614.498 29.743 Pupil dia. (mm)  4.000 r₁ = 99.5495 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 10.1706 (aspherical) d₂ = D2 (variable) r₃ =10.3729 (aspherical) d₃ = 4.4126 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−19.6559 (aspherical) d₄ = D4 (aspherical) r₅ = −9.5997 (aspherical) d₅= 1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 9.8997 (aspherical) d₆ =D6 (variable) r₇ = 14.3933 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78r₈ = −15.6309 (aspherical) d₈ = 0.5000 r₉ = 15.7116 (aspherical) d₉ =22.4940 n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.3160 r₁₁ = ∞(field frame) d₁₁ = 3.6826 r₁₂ = 27.7932 (aspherical) d₁₂ = 16.0681n_(d12) = 1.52542 ν_(d12) = 55.78 r₁₃ = −173.7673 d₁₃ = 2.3552 r₁₄ =35.5235 d₁₄ = 4.0389 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −14.3073(aspherical) d₁₅ = 22.5403 r₁₆ = ∞ (eyepoint) Aspherical coefficientsSecond surface K = −1.3005 A₄ = 6.14835 × 10⁻⁵ A₆ = −1.68311 × 10⁻⁶ A₈ =8.77195 × 10⁻⁹ Third surface K = −0.2546 A₄ = −2.04009 × 10⁻⁶ A₆ =−1.97626 × 10⁻⁶ A₈ = 8.97003 × 10⁻⁹ Fourth surface K = −0.0188 A₄ =1.56534 × 10⁻⁴ A₆ = −1.56324 × 10⁻⁶ A₈ = 1.26722 × 10⁻⁸ Fifth surface K= 0.2126 A₄ = 4.66912 × 10⁻⁴ A₆ = −3.86240 × 10⁻⁵ A₈ = 1.14314 × 10⁻⁶Sixth surface K = −0.0436 A₄ = −2.20422 × 10⁻⁴ A₆ = −2.72889 × 10⁻⁵ A₈ =8.43830 × 10⁻⁷ Eighth surface K = 0.1534 A₄ = 2.24324 × 10⁻⁴ A₆ =−3.90532 × 10⁻⁶ A₈ = 2.12435 × 10⁻⁸ Ninth surface K = 0.0178 A₄ =4.50620 × 10⁻⁵ A₆ = −3.09867 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ =−7.56343 × 10⁻⁴ A₆ = 8.42941 × 10⁻⁷ Fifteenth surface K = 0.0000 A₄ =3.82666 × 10⁻⁵ A₆ = 2.37037 × 10⁻⁷ Wide-angle position Middle positionTelephoto position Zoom data D2   11.1798    6.8982    3.2011 D4   1.7379    8.5495   16.3243 D6    7.6797    5.1496    1.0719 mh =9.800 mm f123 −10.319 −19.589 −41.128 m23    0.530    1.000    2.048 m2 −1.000 m3  −1.000 Condition (9) MG45 −0.744  −0.746  −0.749 Conditions(1), (7) mh/fe = 0.557 Conditions (2), (3) fe = 17.593 mm Condition (8)Φ(mh/2) = −0.484313 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2= −0.309 Condition (12) f2/f3 = −1.663 Condition (13) fw/fFw = −0.742Condition (14) fT/fFT = −0.723 Condition (15) mT/mW = 3.885 Condition(16) fw/fw123 = −0.742 Condition (17) fT/fT123 = −0.723

[0493] Nineteenth Embodiment

[0494] In the real image mode finder optical system of this embodiment,as shown in FIGS. 62A-62C, the objective optical system includes, inorder from the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and the fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0495] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the prism P and the positivelens E1 and has a positive refracting power as a whole.

[0496] The image erecting means includes the prisms P1 and P2 and theprism P. In the real image mode finder optical system of the nineteenthembodiment, the intermediate image formed by the objective opticalsystem is interposed between the prism P2 and the prism P, and the fieldframe, such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

[0497] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis. In this case, the second unit G2 issimply moved toward the object side, and the third unit G3 toward theeyepiece side.

[0498] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havecurvatures. The entrance surface and the exit surface of the prism Palso have curvatures.

[0499] The prisms P1 and P2 and the prism P are provided with the samereflecting surfaces as the reflecting surfaces P1 ₁, P2 ₁, P2 ₂, and P₁in the first embodiment shown in FIGS. 1-3, along the optical path, sothat the optical axis is bent to erect an image. For example, onereflecting surface provided in the prism P1 bends the optical axis inthe Y-Z plane; two reflecting surfaces provided in the prism P2 bend theoptical axis in the Y-Z plane and the X-Z plane in this order from theobject side; and one reflecting surface provided in the prism P bendsthe optical axis in the X-Z plane. In this way, an erect image isobtained. Also, the arrangement of the reflecting surfaces is based onthat of a Porro prism. Angles made with the optical axis bent by thereflecting surfaces are such that, for example, the angles of theoptical axis bent by the reflecting surfaces of the prism P1 and theprism P are smaller than 90 degrees and the angles of the optical axisbent by the reflecting surfaces of the prism P2 are larger than 90degrees. The reflecting surfaces of the prism P1 and the prism P arecoated with metal films, such as silver and aluminum. The two reflectingsurfaces of the prism P2 utilize total reflection.

[0500] However, the ways of bending the optical axis through the prismsand the angles of the optical axis bent by the reflecting surfaces arenot limited to the above description. For example, the angle of theoptical axis bent by the most field-frame-side reflecting surface of theprism P2 may be made smaller than 90 degrees so that this reflectingsurface is coated with a metal film. Moreover, the angle of the opticalaxis bent by the reflecting surface of the prism P may also be madelarger than 90 degrees so that this reflecting surface utilizes totalreflection.

[0501] The positive lens E1 is constructed so that diopter adjustmentcan be made in accordance with an observer's diopter.

[0502] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the nineteenthembodiment are shown below.

[0503] Numerical Data 19 Wide-angle position Middle position Telephotoposition m  0.528  1.033  2.073 ω (°) 33.663 17.287  8.778 f (mm)  7.92715.503 31.114 Pupil dia. (mm)  4.000 r₁ = 38.8071 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 8.9754 (aspherical) d₂ = D2 (variable) r₃ =9.9087 (aspherical) d₃ = 4.3628 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−23.7155 (aspherical) d₄ = D4 (variable) r₅ = −10.0428 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3428 (aspherical) d₆ = D6(variable) r₇ = 11.5157 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−22.7435 (aspherical) d₈ = 0.5000 r₉ = 15.4370 (aspherical) d₉ = 22.2718n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.1155 r₁₁ = ∞ (fieldframe) d₁₁ = 2.3895 r₁₂ = 18.2155 (aspherical) d₁₂ = 15.5672 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −36.4337 d₁₃ = 1.8054 r₁₄ = 26.1660 d₁₄ =4.9762 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −16.4971 (aspherical) d₁₅= 16.9055 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2947 A₄ = 2.38204 × 10⁻⁵ A₆ = 4.87600 × 10⁻⁷ A₈ = −3.73584 × 10⁻⁹Third surface K = −0.2620 A₄ = −1.35699 × 10⁻⁴ A₆ = 4.65011 × 10⁻⁷ A₈ =−1.87327 × 10⁻⁸ Fourth surface K = −0.0225 A₄ = 4.04582 × 10⁻⁵ A₆ =7.12976 × 10⁻⁸ A₈ = −9.76450 × 10⁻⁹ Fifth surface K = 0.2139 A₄ =6.19005 × 10⁻⁴ A₆ = −3.14679 × 10⁻⁵ A₈ = 7.58697 × 10⁻⁷ Sixth surface K= −0.0424 A₄ = 4.58626 × 10⁻⁵ A₆ = −2.40512 × 10⁻⁵ A₈ = 5.34729 × 10⁻⁷Eighth surface K = 0.1566 A₄ = 2.05649 × 10⁻⁴ A₆ = 2.93949 × 10⁻⁷ A₈ =2.68796 × 10⁻⁸ Ninth surface K = 0.0143 A₄ = 7.12313 × 10⁻⁶ A₆ =−6.74794 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ = −1.15138 × 10⁻³ A₆ =8.42829 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ = 4.56110 × 10⁻⁵ A₆ =1.18793 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2   11.7539    7.0573    3.4654 D4    1.2500    8.5614  16.1337 D6    8.1857    5.3729    1.0000 mh = 10.076 mm f123 −10.700−21.016 −43.277 m23    0.529    1.032    2.072 m2  −1.000 m3  −1.032Condition (9) MG45 −0.743  −0.744  −0.746 Conditions (1), (7) mh/fe =0.671 Conditions (2), (3) fe = 15.009 mm Condition (8) Φ(mh/2) =−0.451821 (l/mm) Condition (10) β3 = −1.032 Condition (11) SF2 = −0.411Condition (12) f2/f3 = −1.625 Condition (13) fw/fFw = −0.741 Condition(14) fT/fFT = −0.719 Condition (15) mT/mW = 3.925 Condition (16)fw/fw123 = −0.741 Condition (17) fT/fT123 = −0.719

[0504] Twentieth Embodiment

[0505] The real image mode finder optical system of this embodiment, asshown in FIGS. 63A-63C, has nearly the same arrangement as that of thenineteenth embodiment with the exception of lens data. A substantialdifference with the nineteenth embodiment is that the exit surface ofthe prism P2 has a curvature in twentieth embodiment.

[0506] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the twentiethembodiment are shown below.

[0507] Numerical Data 20 Wide-angle position Middle position Telephotoposition m  0.557  1.038  2.023 ω (°) 32.360 17.517  9.010 f (mm)  8.35615.584 30.363 Pupil dia. (mm)  4.000 r₁ = 59.2465 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 8.3310 (aspherical) d₂ = D2 (variable) r₃ =8.3856 (aspherical) d₃ = 4.1672 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ =−17.8798 d₄ = D4 (variable) r₅ = −13.7008 d₅ = 0.7000 n_(d5) = 1.58423ν_(d5) = 30.49 r₆ = 8.6409 (aspherical) d₆ = D6 (variable) r₇ = 11.7739d₇ = 9.8661 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −29.5195 (aspherical)d₈ = 1.0000 r₉ = 15.0708 d₉ = 22.3752 n_(d9) = 1.52542 ν_(d9) = 55.78r₁₀ = −416.8001 d₁₀ = 2.0410 r₁₁ = ∞ (field frame) d₁₁ = 2.4340 r₁₂ =15.7244 (aspherical) d₁₂ = 18.3578 n_(d12) = 1.52542 ν_(d12) = 55.78 r₁₃= −20.5538 d₁₃ = 1.2739 r₁₄ = 30.8079 (aspherical) d₁₄ = 3.4263 n_(d14)= 1.52542 ν_(d14) = 55.78 r₁₅ = −24.2754 (aspherical) d₁₅ = 15.7651 r₁₆= ∞ (eyepoint) Aspherical coefficients Second surface K = −1.3070 A₄ =−5.42129 × 10⁻⁵ A₆ = 2.66433 × 10⁻⁶ A₈ = −1.96586 × 10⁻⁸ Third surface K= −0.2445 A₄ = −3.33944 × 10⁻⁴ A₆ = 3.11379 × 10⁻⁷ A₈ = −1.64750 × 10⁻⁸Sixth surface K = −0.0650 A₄ = −5.31385 × 10⁻⁴ A₆ = 4.99350 × 10⁻⁶ A₈ =−6.09994 × 10⁻⁸ Eighth surface K = 0.1673 A₄ = 2.10857 × 10⁻⁴ A₆ =1.83918 × 10⁻⁷ A₈ = 3.12747 × 10⁻⁸ Twelfth surface K = 0.0000 A₄ =−1.45924 × 10⁻³ A₆ = 1.59291 × 10⁻⁵ Fourteenth K = 0.0000 A₄ = 7.03020 ×10⁻⁵ A₆ = 4.89240 × 10⁻⁷ Fifteenth K = 0.0000 A₄ = 8.28668 × 10⁻⁵ A₆ =3.99233 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2   11.8115    7.0078    2.9081 D4    1.0094    6.6799  14.3532 D6    7.7860    4.6744    1.0000 mh = 9.992 mm f123 −12.274−23.044 −46.120 m23    0.734    1.370    2.676 m2  −1.000 m3  −1.370Condition (9) MG45 −0.683  −0.683  −0.683 Conditions (1), (7) mh/fe =0.666 Conditions (2), (3) fe = 15.010 mm Condition (8) Φ(mh/2) =−0.322195 (l/mm) Condition (10) β3 = −1.370 Condition (11) SF2 = −0.361Condition (12) f2/f3 = −1.364 Condition (13) fw/fFw = −0.681 Condition(14) fT/fFT = −0.658 Condition (15) mT/mW = 3.634 Condition (16)fw/fw123 = −0.681 Condition (17) fT/fT123 = −0.658

[0508] Twenty-First Embodiment

[0509] In the real image mode finder optical system of this embodiment,as shown in FIGS. 64A-64C, the objective optical system includes, inorder from the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and the fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0510] The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the prism P and the positivelens E1 and has a positive refracting power as a whole.

[0511] The image erecting means includes the prisms P1 and P2 and theprism P. In the real image mode finder optical system of thetwenty-first embodiment, the intermediate image formed by the objectiveoptical system is interposed between the prism P2 and the positive lensE1, and the field frame, such as that shown in FIG. 4, is provided inthe proximity of its imaging position.

[0512] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by simply moving the second unit G2 towardthe object side and the third unit G3 toward the eyepiece side along theoptical axis.

[0513] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havecurvatures. The entrance surface and the exit surface of the prism Palso have curvatures.

[0514] The prisms P1 and P2 and the prism P, as shown in FIGS. 65-67,are provided with reflecting surfaces P1 ₁, P2 ₁, P2 ₂, and P₁ along theoptical path so that the optical axis is bent to erect an image.Specifically, as shown in FIG. 66, the reflecting surface P1 ₁ providedin the prism P1 bends the optical axis in a Y-Z plane; as shown in FIG.67, the two reflecting surfaces P2 ₁ and P2 ₂ provided in the prism P2bend the optical axis twice in the X-Y plane in this order from theobject side; and as shown in FIG. 66, the reflecting surface P₁ providedin the prism P bends the optical axis in the Y-Z plane. In this way, anerect image is obtained. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are 90 degrees. The reflectingsurfaces P1 ₁, P2 ₁, and P2 ₂ of the prism P1 and the prism P2 arecoated with metal films, such as silver and aluminum. The reflectingsurface P₁ of the prism P utilizes total reflection.

[0515] However, the ways of bending the optical axis through the prismsand the angles of the optical axis bent by the reflecting surfaces arenot limited to the above description. For example, the angle of theoptical axis bent by one reflecting surface of the prism P2 may be madesmaller than 90 degrees so that this reflecting surface is coated with ametal film. Moreover, the angle of the optical axis bent by the otherreflecting surface of the prism P2 may also be made larger than 90degrees so that this reflecting surface utilizes total reflection.

[0516] The positive lens E1 is constructed so that diopter adjustmentcan be made in accordance with an observer's diopter.

[0517] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the twenty-firstembodiment are shown below.

[0518] Numerical Data 21 Wide-angle position Middle position Telephotoposition m  0.394  0.659  1.049 ω (°) 32.118 19.007 12.091 f (mm)  6.86611.492 18.288 Pupil dia. (mm)  5.000 r₁ = −59.3919 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 10.3748 8 (aspherical) d₂ = D2 (variable) r₃= 14.1522 (aspherical) d₃ = 3.7000 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−9.2660 (aspherical) d₄ = D4 (variable) r₅ = −7.5095 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 13.7636 d₆ = D6 (variable)r₇ = 20.3870 d₇ = 10.0000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −13.4385(aspherical) d₈ = 0.4000 r₉ = 12.4702 (aspherical) d₉ = 22.0000 n_(d9) =1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.0000 r₁₁ = ∞ (field frame) d₁₁ =7.9991 r₁₂ = −18.8914 (aspherical) d₁₂ = 3.1688 n_(d12) = 1.52542ν_(d12) = 55.78 r₁₃ = −15.1681 d₁₃ = 2.0000 r₁₄ = −13.4956 (aspherical)d₁₄ = 12.2000 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −10.7971(aspherical) d₁₅ = 13.5000 r₁₆ = ∞ (eyepoint) Aspherical coefficientsSecond surface K = −1.8801 A₄ = 8.93195 × 10⁻⁵ A₆ = −1.59803 × 10⁻⁵ A₈ =2.26734 × 10⁻⁷ Third surface K = −26.0761 A₄ = 8.01991 × 10⁻⁴ A₆ =−1.09865 × 10⁻⁴ A₈ = 4.19307 × 10⁻⁶ A₁₀ = −1.65929 × 10⁻⁷ Fourth surfaceK = −0.7079 A₄ = 1.90150 × 10⁻⁴ A₆ = −3.87917 × 10⁻⁵ A₈ = 8.76025 × 10⁻⁷A₁₀ = −3.24756 × 10⁻⁸ Fifth surface K = −0.4742 A₄ = 4.50016 × 10⁻⁴ A₆ =4.48738 × 10⁻⁵ A₈ = −3.79556 × 10⁻⁶ Eighth surface K = 0.8140 A₄ =−1.12430 × 10⁻³ A₆ = 5.37408 × 10⁻⁵ A₈ = −1.01121 × 10⁻⁶ Ninth surface K= −2.4434 A₄ = −1.05938 × 10⁻³ A₆ = 4.60167 × 10⁻⁵ A₈ = −8.38383 × 10⁻⁷Twelfth surface K = 0.0000 A₄ = 4.97477 × 10⁻⁴ A₆ = −3.14535 × 10⁻⁵ A₈ =−3.04078 × 10⁻⁸ Fourteenth surface K = 0.0000 A₄ = −8.27827 × 10⁻⁴ A₆ =5.41341 × 10⁻⁵ A₈ = −6.06561 × 10⁻⁷ Fifteenth surface K = 0.0000 A₄ = −4.89807 × 10⁻⁶ A₆ = 7.07749 × 10⁻⁶ A₈ = −9.70475 × 10⁻⁸ Wide-angleposition Middle position Telephoto position Zoom data D2   8.2666   5.9354    3.4477 D4   0.8000    5.6220   10.2589 D6   5.3399   2.8492    0.7000 mh = 10.139 mm f123 −9.787 −16.419 −26.311 m23  0.651    1.088    1.729 m2  −1.000 m3  −1.088 Condition (9) MG45−0.703  −0.704  −0.705 Conditions (1), (7) mh/fe = 0.473 Conditions (2),(3) fe = 17.434 mm Condition (10) β3 = −1.088 Condition (11) SF2 = 0.209Condition (12) f2/f3 = −1.379 Condition (13) fw/fFw = −0.702 Condition(14) fT/fFT = −0.695 Condition (15) mT/mW = 2.663 Condition (16)fw/fw123 = −0.702 Condition (17) fT/fT123 = −0.695

[0519] Twenty-Second Embodiment

[0520] In the real image mode finder optical system of this embodiment,as shown in FIGS. 68A-68C, the objective optical system includes, inorder from the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and the fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0521] The fourth unit G4 is constructed with the positive lens L1 andthe prism P1. The eyepiece optical system is constructed with the prismP and the positive lens E1 and has a positive refracting power as awhole.

[0522] The image erecting means includes the prism P1 and the prism P.In the real image mode finder optical system of the second embodiment,the intermediate image formed by the objective optical system isinterposed between the prism P1 and the prism P, and the field frame,such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

[0523] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by simply moving the second unit G2 towardthe object side and the third unit G3 toward the eyepiece side along theoptical axis.

[0524] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface of the prismP1 has a curvature. The entrance surface and the exit surface of theprism P also have curvatures.

[0525] The prism P1 and the prism P are provided with reflectingsurfaces along the optical path so that the optical axis is bent toobtain an erect image. For example, the prism P1 is provided with threereflecting surfaces for bending the optical axis twice in the Y-Z planeand once in the X-Z plane in this order from the object side, and theprism P is provided with one reflecting surface for bending the opticalaxis in the X-Z plane to erect the image. Also, the arrangement of thereflecting surfaces is based on that of a Porro prism. Angles made withthe optical axis bent by the reflecting surfaces are such that, forexample, the angle of the optical axis bent by one reflecting surface ofthe prism P1 is smaller than 90 degrees and the angles of the opticalaxis bent by the remaining two reflecting surfaces are larger than 90degrees, while the angle of the optical axis bent by the reflectingsurface of the prism P is smaller than 90 degrees. The reflectingsurfaces making angles smaller than 90 degrees are coated with metalfilms, such as silver and aluminum. The reflecting surfaces of angleslarger than 90 degrees utilize total reflection.

[0526] However, the angles of the optical axis bent by the reflectingsurfaces are not limited to the above description. For example, theangle of the optical axis bent by the most field-frame-side reflectingsurface of the prism P1 may be made smaller than 90 degrees so that thisreflecting surface is coated with a metal film. Moreover, the angle ofthe optical axis bent by the reflecting surface of the prism P may alsobe made larger than 90 degrees so that this reflecting surface utilizestotal reflection.

[0527] The positive lens E1 is constructed so that diopter adjustmentcan be made in accordance with an observer's diopter.

[0528] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the twenty-secondembodiment are shown below.

[0529] Numerical Data 22 Wide-angle position Middle position Telephotoposition m  0.710  1.045  2.031 ω (°) 26.166 17.592  9.011 f (mm) 10.64715.663 30.438 Pupil dia. (mm)  4.000 r₁ = 94.9717 d₁ = 0.9721 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 9.3965 (aspherical) d₂ = D2 (variable) r₃ =9.8091 (aspherical) d₃ = 4.2874 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−25.4274 (aspherical) d₄ = D4 (variable) r₅ = −16.9121 d₅ = 1.0000n_(d5) = 1.58423 ν_(d5) = 30.49 r₆ = 15.2040 (aspherical) d₆ = D6(variable) r₇ = 40.9744 d₇ = 3.5824 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−14.7461 (aspherical) d₈ = 0.5000 r₉ = 21.4998 (aspherical) d₉ = 28.4133n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 1.8195 r₁₁ = ∞ (fieldframe) d₁₁ = 2.3065 r₁₂ = 15.5002 (aspherical) d₁₂ = 15.7893 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −35.0088 d₁₃ = 1.9666 r₁₄ = 27.5692(aspherical) d₁₄ = 5.0860 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ =−16.2713 (aspherical) d₁₅ = 16.9035 r₁₆ = ∞ (eyepoint) Asphericalcoefficients Second surface K = −1.2960 A₄ = 2.42034 × 10⁻⁵ A₆ =−4.03294 × 10⁻⁷ A₈ = −3.85761 × 10⁻¹⁰ Third surface K = −0.2523 A₄ =−1.40079 × 10⁻⁴ A₆ = 9.09631 × 10⁻⁸ A₈ = −7.25698 × 10⁻⁹ Fourth surfaceK = −0.0226 A₄ = 2.34829 × 10⁻⁵ A₆ = 6.60458 × 10⁻⁷ A₈ = −6.09388 × 10⁻⁹Sixth surface K = −0.0504 A₄ = −1.07083 × 10⁻⁴ A₆ = 1.32744 × 10⁻⁶ A₈ =−4.22406 × 10⁻⁹ Eighth surface K = 0.1637 A₄ = 5.89020 × 10⁻⁵ A₆ =2.51165 × 10⁻⁷ A₈ = 1.03528 × 10⁻⁸ Ninth surface K = 0.0039 A₄ =−3.04882 × 10⁻⁶ A₆ = 4.78283 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ =−1.19998 × 10⁻³ A₆ = 1.07234 × 10⁻⁵ Fourteenth surface K = 0.0000 A₄ =3.35581 × 10⁻⁵ A₆ = −1.60128 × 10⁻⁷ Fifteenth surface K = 0.0000 A₄ =7.31972 × 10⁻⁵ A₆ = 9.93972 × 10⁻⁹ Wide-angle position Middle positionTelephoto position Zoom data D2  8.3076  6.0828  3.0961 D4  1.1490 6.5799  16.8299 D6  11.9688  8.7628  1.4995 mh = 9.844 mm f123 −21.628−32.011 −64.323 m23  1.204  1.771  3.458 m2  −1.328 m3  −1.333 Condition(9) MG45 −0.495  −0.495  −0.495 Conditions (1), (7) mh/fe = 0.657Conditions (2), (3) fe = 14.990 mm Condition (11) SF2 = −0.443 Condition(12) F2/f3 = −1.038 Condition (13) fw/fFw = −0.492 Condition (14) fT/fFT= −0.473 Condition (15) mT/mW = 2.859 Condition (16) fw/fw123 = −0.492Condition (17) fT/fT123 = −0.473

[0530] Twenty-Third Embodiment

[0531] The real image mode finder optical system of this embodiment, asshown in FIGS. 69A-69C, has nearly the same arrangement as that of thetwenty-first embodiment with the exception of lens data.

[0532] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the twenty-thirdembodiment are shown below.

[0533] Numerical Data 23 Wide-angle position Middle position Telephotoposition m  0.574  0.905  1.568 ω (°) 24.652 15.498  8.841 f (mm) 10.61716.725 28.996 Pupil dia. (mm)  4.000 r₁ = −920.9537 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 9.9330 (aspherical) d₂ = D2 (variable) r₃ =9.6882 (aspherical) d₃ = 4.1510 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−23.0106 (aspherical) d₄ = D4 (variable) r₅ = −14.4812 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 14.7812 (aspherical) d₆ = D6(variable) r₇ = 11.6881 d₇ = 10.4000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈= −44.1162 (aspherical) d₈ = 0.5000 r₉ = 19.0394 (aspherical) d₉ =21.0918 n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.9577 r₁₁ = ∞(field frame) d₁₁ = 8.6051 r₁₂ = 18.8914 (aspherical) d₁₂ = 3.0466n_(d12) = 1.52542 ν_(d12) = 55.78 r₁₃ = −19.3762 d₁₃ = 2.5000 r₁₄ =−22.1615 (aspherical) d₁₄ = 14.0000 n_(d14) = 1.52542 ν_(d14) = 55.78r₁₅ = −13.1330 (aspherical) d₁₅ = 16.9541 r₁₆ = ∞ (eyepoint) Asphericalcoefficients Second surface K = −1.2958 A₄ = −1.37883 × 10⁻⁴ A₆ =3.49813 × 10⁻⁶ A₈ = −2.85996 × 10⁻⁸ Third surface K = −0.2610 A₄ =−2.84178 × 10⁻⁴ A₆ = 2.18425 × 10⁻⁶ A₈ = 1.89724 × 10⁻⁸ Fourth surface K= −0.0222 A₄ = −3.94404 × 10⁻⁵ A₆ = 2.36146 × 10⁻⁶ A₈ = 1.07129 × 10⁻⁸Fifth surface K = 0.2136 A₄ = 7.49839 × 10⁻⁴ A₆ = −3.41182 × 10⁻⁵ A₈ =9.01815 × 10⁻⁷ Sixth surface K = −0.0419 A₄ = 6.33920 × 10⁻⁴ A₆ =−3.96052 × 10⁻⁵ A₈ = 1.13002 × 10⁻⁶ Eighth surface K = 0.1567 A₄ =1.02994 × 10⁻⁴ A₆ = 3.46598 × 10⁻⁶ A₈ = 6.31270 × 10⁻⁹ Ninth surface K =0.0129 A₄ = −6.13561 × 10⁻⁵ A₆ = 1.96098 × 10⁻⁶ Twelfth surface K =0.0000 A₄ = −1.14754 × 10⁻⁴ A₆ = 2.96268 × 10⁻⁶ A₈ = −4.33585 × 10⁻⁸Fourteenth surface K = 0.0000 A₄ = −1.44350 × 10⁻⁴ A₆ = −3.21946 × 10⁻⁶A₈ = 6.14512 × 10⁻⁸ Fifteenth surface K = 0.0000 A₄ = −7.32422 × 10⁻⁶ A₆= 5.88495 × 10⁻⁷ A₈ = −9.09150 × 10⁻¹⁰ Wide-angle position Middleposition Telephoto position Zoom data D2  8.4479  5.9380  3.5969 D4 2.3409  8.3613  16.2888 D6  10.0702  6.5597  0.9733 mh = 9.332 mm f123−20.012 −31.646 −56.048 m23  1.168  1.864  3.229 m2  −1.365 m3  −1.365Condition (9) MG45  −0.533  −0.535  −0.537 Conditions (1), (7) mh/fe =0.505 Conditions (2), (3) fe = 18.490 mm Condition (11) SF2 = −0.407Condition (12) F2/f3 = −1.097 Condition (13) fw/fFw = −0.530 Condition(14) fT/fFT = −0.517 Condition (15) mT/mW = 2.731 Condition (16)fw/fw123 = −0.530 Condition (17) fT/fT123 = −0.517

[0534] Twenty-Fourth Embodment

[0535] In the real image mode finder optical system of this embodiment,as shown in FIGS. 70A-70C, the objective optical system includes, inorder from the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and the fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

[0536] The fourth unit G4 is constructed with the positive lens L1 andthe prism P1. The eyepiece optical system is constructed with thepositive lens E1 and the prism P and has a positive refracting power asa whole.

[0537] The image erecting means includes the prism P1 and the prism P.In the real image mode finder optical system of the twenty-fourthembodiment, the intermediate image formed by the objective opticalsystem is interposed between the prism P1 and the positive lens E1, andthe field frame, such as that shown in FIG. 4, is provided in theproximity of its imaging position.

[0538] The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by simply moving the second unit G2 towardthe object side and the third unit G3 toward the eyepiece side along theoptical axis.

[0539] Each of the first unit G1, the second unit G2, and the third unitG3 is constructed with a single lens. The entrance surface of the prismP1 has a curvature. The entrance surface and the exit surface of theprism P also have curvatures.

[0540] The prism P1 and the prism P are provided with reflectingsurfaces along the optical path so that the optical axis is bent toobtain an erect image. For example, the prism P1 is provided with threereflecting surfaces for bending the optical axis once in the Y-Z planeand twice in the X-Y plane in this order from the object side, and theprism P is provided with one reflecting surface for bending the opticalaxis in the Y-Z plane to erect the image. Also, the arrangement of thereflecting surfaces is based on that of a Porro prism. Angles made withthe optical axis bent by the reflecting surfaces are such that, forexample, the angles of the optical axis bent by the reflecting surfacesof the prism P1 are smaller than 90 degrees. The three reflectingsurfaces of the prism P1 are coated with metal films, such as silver andaluminum. The reflecting surface of the prism P utilizes totalreflection.

[0541] However, the ways of bending the optical axis through the prismsand the angles of the optical axis bent by the reflecting surfaces arenot limited to the above description. For example, the angle of theoptical axis bent by the most field-frame-side reflecting surface of theprism P1 may be made smaller than 90 degrees so that this reflectingsurface is coated with a metal film. Moreover, the angle of the opticalaxis bent by the second reflecting surface, from the field frame side,of the prism P1 may also be made larger than 90 degrees so that thisreflecting surface utilizes total reflection.

[0542] The positive lens E1 is constructed so that diopter adjustmentcan be made in accordance with an observer's diopter.

[0543] Subsequently, numerical data of optical members constituting thereal image mode finder optical system according to the twenty-fourthembodiment are shown below.

[0544] Numerical Data 24 Wide-angle position Middle position Telephotoposition m  0.457  0.775  1.602 ω (°) 30.208 17.858  8.701 f (mm)  8.50514.412 29.797 Pupil dia. (mm)  4.000 r₁ = 75.2465 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 8.8816 (aspherical) d₂ = D2 (variable) r₃ =10.2728 (aspherical) d₃ = 4.1473 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−18.0037 (aspherical) d₄ = D4 (variable) r₅ = −10.0864 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3864 (aspherical) d₆ = D6(variable) r₇ = 19.6921 d₇ = 4.3014 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−13.1461 (aspherical) d₈ = 0.5000 r₉ = 21.4624 (aspherical) d₉ = 27.5577n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.1330 r₁₁ = ∞ (fieldframe) d₁₁ = 8.3794 r₁₂ = 18.8914 (aspherical) d₁₂ = 3.1249 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −18.8429 d₁₃ = 2.5000 r₁₄ = −19.8984(aspherical) d₁₄ = 14.0000 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ =−12.6982 (aspherical) d₁₅ = 16.9541 r₁₆ = ∞ (eyepoint) Asphericalcoefficients Second surface K = −1.2958 A₄ = 3.44925 × 10⁻⁶ A₆ = 4.20426× 10⁻⁷ A₈ = −7.66223 × 10⁻⁹ Third surface K K = −0.2616 A₄ = −2.70426 ×10⁻⁴ A₆ = 1.77644 × 10⁻⁶ A₈ = −2.00847 × 10⁻⁷ Fourth surface K K =−0.0223 A₄ = −7.38297 × 10⁻⁵ A₆ = 6.70806 × 10⁻⁷ A₈ = −1.54652 × 10⁻⁷Fifth surface K K = 0.2135 A₄ = 3.49998 × 10⁻⁴ A₆ = −1.71207 × 10⁻⁵ A₈ =3.68862 × 10⁻⁷ Sixth surface K K = −0.0430 A₄ = −1.78394 × 10⁻⁴ A₆ =−7.98576 × 10⁻⁶ A₈ = 1.76981 × 10⁻⁷ Eighth surface K K = 0.1579 A₄ =4.99038 × 10⁻⁶ A₆ = 8.82927 × 10⁻⁷ A₈ = 1.18585 × 10⁻⁸ Ninth surface K K= 0.0120 A₄ = −1.28730 × 10⁻⁴ A₆ = 5.21275 × 10⁻⁷ Twelfth surface K K =0.0000 A₄ = −2.49634 × 10⁻⁴ A₆ = 1.72455 × 10⁻⁷ A₈ = 2.31794 × 10⁻⁹Fourteenth surface K K = 0.0000 A₄ = 8.06332 × 10⁻⁶ A₆ = 4.07603 × 10⁻⁷A₈ = −1.41628 × 10⁻⁸ Fifteenth surface K K = 0.0000 A₄ = 3.96776 × 10⁻⁵A₆ = 5.11111 × 10⁻⁸ A₈ = −1.38979 × 10⁻¹⁰ Wide-angle position Middleposition Telephoto position Zoom data D2  11.4348  8.0329  4.3575 D4 1.2500  6.8862  14.8224 D6  8.1779  5.9436  1.6828 mh = 9.391 mm f123−10.255 −17.402 −36.720 m23  0.592  1.000  2.070 m2  −1.000 m3  −1.000Condition (9) MG45 −0.831  −0.834  −0.837 Conditions (1), (7) mh/fe =0.505 Conditions (2), (3) fe = 18.603 mm Condition (8) φ(mh/2) =−0.118345 (1/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.273Condition (12) F2/f3 = −1.524 Condition (13) fw/fFw = −0.829 Condition(14) fT/fFT = −0.811 Condition (15) mT/mW = 3.503 Condition (16)fw/fW123 = −0.829 Condition (17) fT/fT123 = −0.811

[0545] The real image mode finder optical system according to thepresent invention constructed as mentoned above can be used in any ofvarious photographing apparatuses, such as compact cameras, for example,35 mm film cameras and APS film cameras; digital cameras usingelectronic image sensors, for example, CCDs and CMOS sensors; and videomovies. A specific application example of this finder optical systemwill be described below.

[0546] FIGS. 71-73 show an example of an electromic camera incorporatingthe real image mode finder optical system of the present invention.

[0547] As shown in FIGS. 71-73, an electronic camera 200 includes aphotographing optical system 202 having a photpgraphing optical path201, a finder optical system 204 of the present invention having afinder optical path 203, a release button 205, a stroboscopic lamp 206,and a liquid crystal display monitor 207. When the release button 205provided on the upper surface of the electronic camera 200 is pushd,photographing is performed through the photographing optical system 202in association with the release button 205. An object image formed bythe photographing optical system 202 falls on an image senser chip 209,such as a CCD, through various filters 208, such as an IR (infrared)cutoff filter and a low-pass filter.

[0548] The object image received by the image sensor chip 209 isdisplayed, as an electronic image, on the liquid crystal display monitor207 provided on the back surface of the electronic camera 200 through aprocessing means 211 electrically connected with terminals 210. Theprocessing means 211 controls a recording means 212 for recording theobject image received by the image sensor chip 209 as electronicinformation. The recording means 212 is electrocally connected with theprocessing means 211. Also, the recording means 212 may be replaced witha device for writing the record in a recording medium, such as a floppydisk, a smart medium, or memory card.

[0549] Where the photographing optical system 202 is constructed as azoom lens, the finder optical system 204 having the finder optical path203 may use the real image mode finder optical system of any of theabove embodiments. Where the photographing optical system 202 is asingle focus optical system, the objective optical system in the finderoptical system 204 may be replaced with a single focus objective opticalsystem in which a photographing area can be observed.

[0550] For the image erecting means, any means which is capable oferecting an image, not to speak of the Porro prism, is satisfactory. Forexample, when a roof reflecting surface is used as the image erectingmeans so that the objective optical system includes the roof reflectingsurface and one planar reflecting surface and the eyepiece opticalsystem includes one planar reflecting surface, compactness of the entirecamera can be achieved. The reflecting surfaces are not limited toplanar surfaces and may be configured as curved surfaces.

[0551] Even when a photographing film is used instead of the imagesensor chip 209, a compact film camera with an excellent view can beobtained.

[0552] FIGS. 74A-74C show a specific example of a photographing zoomlens used in a compact camera for a 35 mm film (the maximum image heightof 21.6 mm).

[0553] The photographing zoom lens includes, in order from the objectside, the first unit G1 with a positive refracting power; the secondunit G2 with a negative refracting power, having an aperture stop Swhich is variable in aperture diameter, at the most object-sideposition; and the third unit G3 with a negative refracting power. Whenthe magnification of the finder is changed in the range from thewide-angle position to the telephoto position, a space between the firstunit and the second unit is continuously widened, and a space betweenthe second unit and the third unit is contunuously narrowed, so that thefirst unit and the third unit are integrally constructed and the firstunit, the second unit, and the third unit are continuously moved towardthe object side, thereby forming the object image on a film surface.

[0554] Subsequently, numerical data of optical members constituting thephotographing zoom lens are shown below. In the numerical data, frepresents the focal length of the photographing zoom lens, ω representsa half angle of view, Fno represents an F-number, and bf represents aback focal distance. Other symbols are the same as those used in thenumerical data of the embodiments.

[0555] Numerical Data (Photographing Zoom Lens) Wide-angle positionMiddle position Telephoto position f (mm) 29.31 72.87 135.00 ω(°) 28.316.1  9.0 Fno  4.1  6.8  11.5 bf (mm)  9.47732 31.48343  71.3185 r₁ =−180.6198 d₁ = 1.2001 n_(d1) = 1.76182 ν_(d1) = 26.52 r₂ = 180.6198 d₂ =0.2286 r₃ = 21.6168 d₃ = 3.1212 n_(d3) = 1.49700 ν_(d3) = 81.54 r₄ =−380.8986 d₄ = D4 (variable) r₅ = ∞ (stop) d₅ = 1.0000 r₆ = −16.3795 d₆= 1.0004 n_(d6) = 1.77250 ν_(d6) = 49.60 r₇ = 12.8963 d₇ = 3.1001 n_(d7)= 1.72825 ν_(d7) = 28.46 r₈ = −134.5936 d₈ = 0.4702 r₉ = 31.9527 d₉ =3.3010 n_(d9) = 1.56016 ν_(d9) = 60.30 r₁₀ = −24.8940 (aspherical) d₁₀ =0.7899 r₁₁ = −80.7304 d₁₁ = 1.0020 n_(d11) = 1.80518 ν_(d11) = 25.43 r₁₂= 21.6465 d₁₂ = 4.0740 n_(d12) = 1.69680 ν_(d12) = 55.53 r₁₃ = −17.2293d₁₃ = D13 (variable) r₁₄ = −48.1099 (aspherical) d₁₄ = 0.2501 n_(d14) =1.52288 ν_(d14) = 52.50 r₁₅ = −65.5251 d₁₅ = 1.3535 n_(d15) = 1.80610ν_(d15) = 40.95 r₁₆ = 47.5056 d₁₆ = 0.2911 r₁₇ = 41.0817 d₁₇ = 3.5899n_(d17) = 1.80518 ν_(d17) = 25.43 r₁₈ = −76.4471 d₁₈ = 3.8912 r₁₉ =−14.7089 d₁₉ = 1.6801 n_(d19) = 1.69680 ν_(d19) = 55.53 r₂₀ = −488.7372d₂₀ = D20 (variable) r₂₁ = ∞ (film surface) Aspherical coefficientsTenth surface K = 1.5373 A₄ = 8.3473 × 10⁻⁵ A₆ = 5.1702 × 10⁻⁷ A₈ =−1.3021 × 10⁻⁸ A₁₀ = 1.5962 × 10⁻¹⁰ Fourteenth surface K = −18.4065 A₄ =2.4223 × 10⁻⁵ A₆ = 1.3956 × 10⁻⁷ A₈ = −1.8237 × 10⁻¹⁰ A₁₀ = 3.9911 ×10⁻¹² Zoom data Wide-angle position Middle position Telephoto positionWhen an infinite object point is focused: D4  3.6815 10.0332 14.0700 D1311.5705  5.2188  1.1820 D20  9.4773 31.4834 71.3185 When the objectpoint distance is 0.6 m: D4  2.3504  8.3489 11.9918 D13 12.9016  6.9031 3.2602 D20  9.4773 31.4834 71.3185

What is claimed is:
 1. A real image mode finder optical systemconstructed to be independent of a photographing optical system,comprising, in order from an object side: an objective optical systemwith a positive refracting power; a field frame located in the proximityof an imaging position of said objective optical system; and an eyepieceoptical system with a positive refracting power, wherein said real imagemode finder optical system includes image erecting means, and a focallength of said objective optical system can be made shorter than a focallength of said eyepiece optical system, said real image mode finderoptical system satisfying the following condition: 0.52<mh/fe<1 where mhis a maximum width of said field frame and fe is a focal length of saideyepiece optical system.
 2. A real image mode finder optical systemcomprising, in order from an object side: an objective optical systemwith a positive refracting power; a field frame located in the proximityof an imaging position of said objective optical system; and an eyepieceoptical system with a positive refracting power, wherein said real imagemode finder optical system includes image erecting means, and saidobjective optical system includes three of reflecting surfaces of saidimage erecting means and said eyepiece optical system includes one ofreflecting surfaces of said image erecting means so that an image iserected through four reflecting surfaces comprised of three reflectingsurfaces of said objective optical system and one reflecting surface ofsaid eyepiece optical system, and wherein a focal length of saidobjective optical system is variable, and when a magnification of saidfinder optical system is changed, at least two lens units are movedalong different paths and a focal length of said objective opticalsystem at a wide-angle position thereof is shorter than a focal lengthof said eyepiece optical system, said real image mode finder opticalsystem satisfying the following condition: 0.52<mh/fe<1 where mh is amaximum width of said field frame and fe is a focal length of saideyepiece optical system.
 3. A real image mode finder optical systemcomprising, in order from an object side: an objective optical systemwith a positive refracting power; a field frame located in the proximityof an imaging position of said objective optical system; and an eyepieceoptical system with a positive refracting power, wherein said real imagemode finder optical system includes image erecting means, and saidobjective optical system includes three of reflecting surfaces of saidimage erecting means and said eyepiece optical system includes one ofreflecting surfaces of said image erecting means so that an image iserected through four reflecting surfaces comprised of three reflectingsurfaces of said objective optical system and one reflecting surface ofsaid eyepiece optical system, wherein a focal length of said objectiveoptical system is variable, and when a magnification of said finderoptical system is changed, at least two lens units are moved alongdifferent paths and a focal length of said objective optical system at awide-angle position thereof is shorter than a focal length of saideyepiece optical system, and wherein said image erecting means includingsaid three reflecting surfaces of said objective optical system isconstructed with two prisms so that each of said prisms has at least onereflecting surface and one of an entrance surface and an exit surface ofeach prism is configured as a curved surface with finite curvature.
 4. Areal image mode finder optical system comprising, in order from anobject side: an objective optical system with a positive refractingpower; a field frame located in the proximity of an imaging position ofsaid objective optical system; and an eyepiece optical system with apositive refracting power, wherein said objective optical system hasimage erecting means including four reflecting surfaces, and wherein afocal length of said objective optical system is variable, and when amagnification of said finder optical system is changed, at least twolens units are moved along different paths and a focal length of saidobjective optical system at a wide-angle position thereof is shorterthan a focal length of said eyepiece optical system, said real imagemode finder optical system satisfying the following condition:0.52<mh/fe<1 where mh is a maximum width of said field frame and fe is afocal length of said eyepiece optical system.
 5. A real image modefinder optical system comprising, in order from an object side: anobjective optical system with a positive refracting power; a field framelocated in the proximity of an imaging position of said objectiveoptical system; and an eyepiece optical system with a positiverefracting power, wherein said objective optical system has imageerecting means including four reflecting surfaces, and wherein a focallength of said objective optical system is variable, and when amagnification of said finder optical system is changed, at least twolens units are moved along different paths and a focal length of saidobjective optical system at a wide-angle position thereof is shorterthan a focal length of said eyepiece optical system.
 6. A real imagemode finder optical system according to claim 1, wherein a focal lengthof said objective optical system is variable, and when a magnificationof said finder optical system is changed, at least two lens units aremoved along different paths.
 7. A real image mode finder optical systemaccording to claim 1, satisfying the following condition: 12.0mm<fe<18.0 mm
 8. A real image mode finder optical system according toclaim 1, satisfying the following condition: 13.5 mm<fe<16.5 mm
 9. Areal image mode finder optical system according to claim 1, wherein saidobjective optical system includes three of reflecting surfaces of saidimage erecting means and said eyepiece optical system includes one ofreflecting surfaces of said image erecting means so that an image iserected through four reflecting surfaces comprised of three reflectingsurfaces of said objective optical system and one reflecting surface ofsaid eyepiece optical system.
 10. A real image mode finder opticalsystem according to claim 1, wherein said objective optical system hassaid image erecting means including four reflecting surfaces so that animage is erected through said four reflecting surfaces of said objectiveoptical system.
 11. A real image mode finder optical system according toclaim 2, wherein said objective optical system comprises, in order fromsaid object side, a first unit with a negative power, fixed or movedwhen said magnification is changed; a second unit with a positive power,moved when said magnification is changed; a third unit with a negativepower, moved when said magnification is changed; and a fourth unit witha positive power, fixed when said magnification is change and includingthree reflecting surfaces.
 12. A real image mode finder optical systemaccording to claim 11, wherein said fourth unit includes at least oneprism having at least one reflecting surface, and one of an entrancesurface and an exit surface of said prism is configured as a curvedsurface with finite curvature.
 13. A real image mode finder opticalsystem according to claim 11, wherein each of said first unit, saidsecond unit, and said third unit is constructed with a single lens. 14.A real image mode finder optical system according to claim 11, whereinsaid eyepiece optical system includes two optical elements having lensfunctions, providing air spacing between said two optical elements andhas a positive refracting power as a whole.
 15. A real image mode finderoptical system according to claim 14, wherein said eyepiece opticalsystem includes, in order from said object side, a prism which providesan exit surface thereof with a lens function and has a part of an imageerecting function and a single positive lens component.
 16. A real imagemode finder optical system according to claim 15, wherein said prism ofsaid eyepiece optical system has a lens function with respect to anentrance surface thereof.
 17. A real image mode finder optical systemaccording to claim 15, wherein said positive lens component of saideyepiece optical system is constructed so that diopter adjustment can bemade in accordance with an observer's diopter.
 18. A real image modefinder optical system according to claim 2, satisfying the followingcondition: 12.0 mm<fe<18.0 mm
 19. A real image mode finder opticalsystem according to claim 4, wherein said objective optical systemincludes, in order from said object side, a first unit with a negativepower, moved when said magnification is changed; a second unit with apositive power, moved when said magnification is changed; a third unitwith a negative power, moved when said magnification is changed; and afourth unit with a positive power, fixed when said magnification ischange and including three reflecting surfaces.
 20. A real image modefinder optical system according to claim 19, wherein said fourth unitincludes two prisms so that each of said prisms has at least onereflecting surface and one of an entrance surface and an exit surface ofeach prism is configured as a curved surface with finite curvature. 21.A real image mode finder optical system according to claim 20, whereinat least one of said two prisms has totally reflecting surfaces.
 22. Areal image mode finder optical system according to claim 20, whereineach of said first unit, said second unit, and said third unit isconstructed with a single lens.
 23. A photographing apparatus providedwith a real image mode finder optical system comprising, in order froman object side: an objective optical system with a positive refractingpower; a field frame located in the proximity of an imaging position ofsaid objective optical system; and an eyepiece optical system with apositive refracting power, wherein said real image mode finder opticalsystem includes image erecting means, and a focal length of saidobjective optical system can be made shorter than a focal length of saideyepiece optical system, said real image mode finder optical systemsatisfying the following condition: 0.52<mh/fe<1  where mh is a maximumwidth of said field frame and fe is a focal length of said eyepieceoptical system.
 24. A real image mode finder optical system constructedto be independent of a photographing optical system, comprising, inorder from an object side: an objective optical system with a positiverefracting power; a field frame located in the proximity of an imagingposition of said objective optical system; and an eyepiece opticalsystem with a positive refracting power, wherein said real image modefinder optical system includes an image erecting means and wherein saidobjective optical system is capable of having a focal length shorterthan a focal length of said eyepiece optical system, and said eyepieceoptical system has at least one lens element so that a most observer'spupil-side lens element satisfies the following condition: v>70  where vis an Abbe's number of said most observer's pupil-side lens element. 25.A real image mode finder optical system constructed to be independent ofa photographing optical system, comprising, in order from an objectside: an objective optical system with a positive refracting power; afield frame located in the proximity of an imaging position of saidobjective optical system; and an eyepiece optical system with a positiverefracting power, wherein said real image mode finder optical systemincludes an image erecting means and wherein said objective opticalsystem is capable of having a focal length shorter than a focal lengthof said eyepiece optical system, and said eyepiece optical system has atleast one lens element to satisfy the following conditions: 0.52<mh/fe<1v>70  where mh is a maximum width of said field frame, fe is a focallength of said eyepiece optical system, and v is an Abbe's number of amost observer's pupil-side lens element.
 26. A real image mode finderoptical system constructed to be independent of a photographing opticalsystem, comprising, in order from an object side: an objective opticalsystem with a positive refracting power; a field frame located in theproximity of an imaging position of said objective optical system; andan eyepiece optical system with a positive refracting power, whereinsaid real image mode finder optical system includes an image erectingmeans and wherein said objective optical system is capable of having afocal length shorter than a focal length of said eyepiece opticalsystem, and said eyepiece optical system has a cemented lens componentincluding a positive lens element and a negative lens element at a mostobserver's pupil-side position.
 27. A real image mode finder opticalsystem according to claim 25, wherein said focal length of saidobjective optical system is variable, and when a magnification of saidfinder optical system is changed, at least two lens units are movedalong different paths.
 28. A real image mode finder optical systemaccording to claim 25, wherein said objective optical system includesthree of reflecting surfaces of said image erecting means and saideyepiece optical system includes one of reflecting surfaces of saidimage erecting means so that an image is erected through four reflectingsurfaces comprised of three reflecting surfaces of said objectiveoptical system and one reflecting surface of said eyepiece opticalsystem.
 29. A real image mode finder optical system according to claim25, wherein said objective optical system has said image erecting meansincluding four reflecting surfaces so that an image is erected throughsaid four reflecting surfaces of said objective optical system.
 30. Areal image mode finder optical system constructed to be independent of aphotographing optical system, comprising, in order from an object side:an objective optical system with a positive refracting power; a fieldframe located in the proximity of an imaging position of said objectiveoptical system; and an eyepiece optical system with a positiverefracting power, wherein said real image mode finder optical systemincludes an image erecting means and wherein said objective opticalsystem is capable of having a focal length shorter than a focal lengthof said eyepiece optical system, and said eyepiece optical system has acemented lens component including a positive lens element and a negativelens element at a most observer's pupil-side position to satisfy thefollowing condition: 0.52<mh/fe<1  where mh is a maximum width of saidfield frame and fe is a focal length of said eyepiece optical system.31. A real image mode finder optical system according to claim 30,wherein said focal length of said objective optical system is variable,and when a magnification of said finder optical system is changed, atleast two lens units are moved along different paths.
 32. A real imagemode finder optical system according to claim 30, wherein said objectiveoptical system has said image erecting means including four reflectingsurfaces so that an image is erected through said four reflectingsurfaces of said objective optical system.
 33. A photographing apparatusprovided with a real image mode finder optical system constructed to beindependent of a photographing optical system, comprising, in order froman object side: an objective optical system with a positive refractingpower; a field frame located in the proximity of an imaging position ofsaid objective optical system; and an eyepiece optical system with apositive refracting power, wherein said real image mode finder opticalsystem includes an image erecting means and wherein said objectiveoptical system is capable of having a focal length shorter than a focallength of said eyepiece optical system, and said eyepiece optical systemhas at least one lens element so that a most observer's pupil-side lenselement satisfies the following condition: v>70  where v is an Abbe'snumber of said most observer's pupil-side lens element.
 34. A real imagemode finder optical system comprising, in order from an object side; anobjective optical system with a positive refracting power; a field framelocated in the proximity of an imaging position of said objectiveoptical system; and an eyepiece optical system with a positiverefracting power, wherein said real image mode finder optical systemincludes image erecting means, and wherein said objective optical systemincludes, in order from said object side, a first unit with a negativerefracting power, a second unit with a positive refracting power, athird unit with a negative refracting power, and a fourth unit with apositive refracting power so that a magnification of said finder opticalsystem is changed, ranging from a wide-angle position to a telephotoposition, by simply moving said second unit toward said object side andsaid third unit toward said eyepiece optical system to satisfy thefollowing condition: 12.0 mm<fe<18.0 mm  where fe is a focal length ofsaid eyepiece optical system.
 35. A real image mode finder opticalsystem comprising, in order from an object side; an objective opticalsystem with a positive refracting power; a field frame located in theproximity of an imaging position of said objective optical system; andan eyepiece optical system with a positive refracting power, whereinsaid real image mode finder optical system includes image erectingmeans, and wherein said objective optical system includes, in order fromsaid object side, a first unit with a negative refracting power, asecond unit with a positive refracting power, a third unit with anegative refracting power, and a fourth unit with a positive refractingpower so that a magnification of said finder optical system is changed,ranging from a wide-angle position to a telephoto position, by simplymoving said second unit toward said object side and said third unittoward said eyepiece optical system to satisfy the following condition:0.52<mh/fe<1  where mh is a maximum width of said field frame and fe isa focal length of said eye-piece optical system.
 36. A real image modefinder optical system comprising, in order from an object side; anobjective optical system with a positive refracting power; a field framelocated in the proximity of an imaging position of said objectiveoptical system; and an eyepiece optical system with a positiverefracting power, wherein said real image mode finder optical systemincludes image erecting means, and wherein said objective optical systemis capable of having a focal length shorter than a focal length of saideyepiece optical system, and said eyepiece optical system includes, inorder from said object side, a prism unit with a positive refractingpower and a lens unit with a positive refracting power so that a mostfield-frame-side surface of said prism unit with a positive refractingpower has a positive refracting power and is configured as an asphericalsurface with a negative refracting power on a periphery thereof.
 37. Areal image mode finder optical system according to claim 35, whereinsaid eyepiece optical system, in order from said object side, a prismunit with a positive refracting power and a lens unit with a positiverefracting power so that a most field-frame-side surface of said prismunit with a positive refracting power has a positive refracting power onan optical axis thereof and is configured as an aspherical surface witha negative refracting power on a periphery thereof.
 38. A real imagemode finder optical system according to claim 36, wherein said objectiveoptical system has at least two lens units, said focal length of saidobjective optical system is variable, and when said magnification ischanged, at least two lens units are moved along different paths.
 39. Aphotographing apparatus provided with a real image mode finder opticalsystem comprising, in order from an object side: an objective opticalsystem with a positive refracting power; a field frame located in theproximity of an imaging position of said objective optical system; andan eyepiece optical system with a positive refracting power, whereinsaid real image mode finder optical system includes image erectingmeans, and wherein said objective optical system includes, in order fromsaid object side, a first unit with a negative refracting power, asecond unit with a positive refracting power, a third unit with anegative refracting power, and a fourth unit with a positive refractingpower so that a magnification of said finder optical system is changed,ranging from a wide-angle position to a telephoto position, by simplymoving said second unit toward said object side and said third unittoward said eyepiece optical system to satisfy the following condition:12.0 mm<fe<18.0 mm  where fe is a focal length of said eyepiece opticalsystem.
 40. A real image mode finder optical system comprising, in orderfrom an object side: an objective optical system which has a positiverefracting power and changes a magnification of said finder opticalsystem; a field frame located in the proximity of an imaging position ofsaid objective optical system; and an eyepiece optical system with apositive refracting power, wherein said real image mode finder opticalsystem has image erecting means, and wherein said objective opticalsystem includes, in order from said object side, a front unit with anegative refracting power and a rear unit with a positive refractingpower, said front unit being constructed with a plurality of lens unitsso that a magnification of said finder optical system is changed,ranging from a wide-angle position to a telephoto position, by moving atleast two of said plurality of lens units and said rear unit beingconstructed with a plurality of prism units with positive refractingpowers so that at least one of surfaces opposite to one another, of saidplurality of prism units is configured to be convex.
 41. A real imagemode finder optical system comprising, in order from an object side: anobjective optical system which has a positive refracting power andchanges a magnification of said finder optical system; a field framelocated in the proximity of an imaging position of said objectiveoptical system; and an eyepiece optical system with a positiverefracting power, wherein said real image mode finder optical system hasimage erecting means, and wherein said objective optical systemincludes, in order from said object side, a first unit with a negativerefracting power, a second unit with a positive refracting power, athird unit with a negative refracting power, and a fourth unit with apositive refracting power, said fourth unit being comprised of a fourthfront sub-unit and a fourth rear subunit, a magnification of said finderoptical system being changed, ranging from a wide-angle position to atelephoto position, by moving said second unit and said third unit, eachof said first unit, said second unit, and said third unit beingconstructed with a lens, and each of said fourth front sub-unit and saidfourth rear sub-unit being constructed with a prism so that at least oneof surfaces opposite to each other, of said fourth front sub-unit andsaid fourth rear sub-unit is configured to be convex.
 42. A real imagemode finder optical system according to claim 58, wherein said fourthfront sub-unit includes a single prism and has one reflecting surface.43. A real image mode finder optical system according to claim 41,satisfying the following condition: −1.0<MG45<−0.5  where MG45 is acombined imaging magnification of said fourth front sub-unit and saidfourth rear sub-unit at an object distance of 3 m.
 44. A real image modefinder optical system according to claim 41, wherein each of said secondunit and said third unit is constructed with a single lens and satisfiesthe following condition: −1.9<f2/f3<−1.0 where f2 is a focal length ofsaid second unit and f3 is a focal length of said third unit.
 45. A realimage mode finder optical system according to any one of claim 41,satisfying the following condition: 2.7<mT/mW<7.0 where mW is a findermagnification of an entire system at said wide-angle position and mT isa finder magnification of an entire system at said telephoto position.46. A photographing apparatus provided with a real image mode finderoptical system comprising, in order from an object side: an objectiveoptical system which has a positive refracting power and changes amagnification of said finder optical system; a field frame located inthe proximity of an imaging position of said objective optical system;and an eyepiece optical system with a positive refracting power, whereinsaid real image mode finder optical system has image erecting means, andwherein said objective optical system includes, in order from saidobject side, a front unit with a negative refracting power and a rearunit with a positive refracting power, said front unit being constructedwith a plurality of lens units so that a magnification of said finderoptical system is changed, ranging from a wide-angle position to atelephoto position, by moving at least two of said plurality of lensunits and said rear unit being constructed with a plurality of prismunits with positive refracting powers so that at least one of surfacesopposite to one another, of said plurality of prism units is configuredto be convex.
 47. A real image mode finder optical system comprising, inorder from an object side: an objective optical system which has apositive refracting power and changes a magnification of said finderoptical system; a field frame located in the proximity of an imagingposition of said objective optical system; and an eyepiece opticalsystem with a positive refracting power, wherein said real image modefinder optical system has image erecting means, wherein said objectiveoptical system includes, in order from said object side, a first unitwith a negative refracting power, a second unit with a positiverefracting power, a third unit with a negative refracting power, and afourth unit with a positive refracting power so that a magnification ofsaid finder optical system is changed, ranging from a wide-angleposition to a telephoto position, by simply moving said second unittoward said object side and said third unit toward an eyepiece side, andwherein a combined focal length of said first unit, said second unit,and said third unit is negative, and when said magnification is changedover a range from said wide-angle position to said telephoto position, acombined imaging magnification of said second unit and said third unitis 1×.
 48. A real image mode finder optical system according to claim47, satisfying the following condition: −1.2<β3<−0.8 where β3 is animaging magnification of said third unit in a state where an imagingmagnification of said second unit is −1× at an object distance of 3 mwhen said magnification is changed in a range from said wide-angleposition to said telephoto position.
 49. A real image mode finderoptical system according to claim 47, wherein said second unit isconstructed with a single lens and satisfies the following condition:−0.6<SF2<0.6 where SF2=(r3+r4)/(r3−r4), which is a shape factor of saidsecond unit, r3 is a radius of curvature of an object-side surface ofsaid second unit, and r4 is a radius of curvature of an eyepiece-sidesurface of said second unit.
 50. A real image mode finder optical systemaccording to claim 47, wherein each of said second unit and said thirdunit is constructed with a single lens and satisfies the followingcondition: −1.9<f2/f3<−1.0 where f2 is a focal length of said secondunit and f3 is a focal length of said third unit.
 51. A real image modefinder optical system according to claim 47, wherein said fourth unit isfixed when said magnification is changed in a range from said wide-angleposition to said telephoto position.
 52. A real image mode finderoptical system according to claim 47, wherein said fourth unit includestwo optical units with positive refracting powers.
 53. A real image modefinder optical system according to claim 47, wherein said fourth unithas a plurality of reflecting surfaces.
 54. A real image mode finderoptical system according to claim 47, wherein said first unit is alsomoved when said magnification is changed in a range from said wide-angleposition to said telephoto position.
 55. A real image mode finderoptical system according to claim 47, wherein said first unit is fixedwhen said magnification is changed in a range from said wide-angleposition to said telephoto position.
 56. A photographing apparatusprovided with a real image mode finder optical system comprising, inorder from an object side: an objective optical system which has apositive refracting power and changes a magnification of said finderoptical system; a field frame located in the proximity of an imagingposition of said objective optical system; and an eyepiece opticalsystem with a positive refracting power, wherein said real image modefinder optical system has image erecting means, wherein said objectiveoptical system includes, in order from said object side, a first unitwith a negative refracting power, a second unit with a positiverefracting power, a third unit with a negative refracting power, and afourth unit with a positive refracting power so that a magnification ofsaid finder optical system is changed, ranging from a wide-angleposition to a telephoto position, by simply moving said second unittoward said object side and said third unit toward an eyepiece side, andwherein a combined focal length of said first unit, said second unit,and said third unit is negative, and when said magnification is changedover a range from said wide-angle position to said telephoto position, acombined imaging magnification of said second unit and said third unitis 1×.